History Main / KnightsAndKnaves

* A variation on this puzzle appears in ''VideoGame/ZorkZero''. You're eventually forced into line with an executioner, who lets everyone make a last request. If he can fulfill the request, the executioner hangs the prisoner. If he can't do the last request, the executioner cuts the prisoner's head off. This can be solved with a LogicBomb by saying "Executioner, cut my head off". Since he can do it, he has to fulfill the request, but cutting people's heads off is only done if he can't do the request. Plus, it's impossible to hang somebody once they no longer have a head. The executioner gets so confused that the guards tell you to get out of line, and you get to walk free. However, this only works once -- if you are stupid enough to try the executioner again, he'll have gotten wise to this loophole and made an ObviousRulePatch which includes a third method of death, so [[YetAnotherStupidDeath you're dead thanks to trying to push your luck again]].

* This puzzle appears in ''VideoGame/ZorkZero''. The catch here is that which one lies and which one tells the truth is randomized each time you enter the room, and while in the room, ''you're not allowed to save.'' While this can be solved with a LogicBomb, this only works once -- if you are stupid enough to try again, the riddle-makers have gotten wise to this loophole and made an ObviousRulePatch.

* Shows up in ''Film/{{Labyrinth}}''. It's played with, though, as Sarah falls down a trap door behind the door at the precise moment she announces herself triumphant. On the other hand, taking the wrong door is asserted to lead to certain death, so it's entirely possible that Sarah would have been home free had she not [[TemptingFate declared that the riddle was a piece of cake]]. The Labyrinth is a harsh mistress. There are also indications that the puzzle's conditions aren't quite what they're made out to be. The blue guard told Sarah the conditions: "One of us always lies, and one of us always tells the truth." If the conditions were valid, then that particular speaker was the truth-teller. If he was lying, then all bets were off. And this comes after both guards agree that Sarah may only ask ''one'' of them, when if one of them is always honest and the other always a liar, neither of them should agree on ''anything'' at any time. One interpretation of the scene is that the guards are just messing with Sarah and that ''none'' of them actually knows which door leads to the center of the labyrinth.

** There was a brain teaser in a ''Doctor Who'' annual about two captured soldiers (astronauts?) who were told that they could make one statement, If their statement was judged as true they would die by lethal injection, if their statement was judged as false they would die by hanging. They managed to make a single statement that meant the judge had to let them go. The answer? [[spoiler:They make the statement "I will die by hanging" if they hang them that makes the statement true, which should mean the die by lethal injection, which would then make the statement false, which would mean they should die by hanging and so on.]]

* Many puzzle books tend to include variations on this problem. For example, ''[[http://store.doverpublications.com/048647027x.html The Lady or the Tiger?: and Other Logic Puzzles]]'' starts off with signs, later switching to a sane/insane people, then inverts it to people who can only ask questions that may be answered yes or no (specific to the person asking said question).

* A variation of this problem appears as a puzzle in ''VideoGame/EscapeFromMonkeyIsland'', where Guybrush needs to find hidden treasure with the help of two parrots named Huggyn and Kyssin, who are enchanted by voodoo magic to always tell the truth and lie, respectively. The catch with this variation is that you're asking for directions where there are at least three choices at each intersection. Also, the parrots are identical and fly up and off the screen, then come back after answering a question, so you can no longer tell which one tells the truth. [[spoiler:The trick is to intoxicate one of the parrots with caffeine or alcohol, which produces an obvious change in the bird's appearance -- don't worry, it wears off as soon as you finish the puzzle.]]

* ''Series/DoctorWho''

* Played quite straight with three different agents (liar, truth-sayer and alternator) in ''VideoGame/{{Pathologic}}''. Except that you can cheat and use a disguise to figure out which is the liar.

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* ''VideoGame/TheLegendOfZeldaPhantomHourglass'' combines this trope with TenLittleMurderVictims: Amongst the members of the Isle of Frost's Anouki tribe is a Yook, their chief enemy on the island, and he's so well disguised that the only way to identify him is that Anoukis always tell the truth while Yooks always lie.
* In ''Franchise/TheElderScrolls'' series ActionAdventure spin-off ''[[VideoGame/TheElderScrollsAdventuresRedguard Redguard]]'', Clavicus Vile poses this riddle to the protagonist Cyrus. He's GenreSavvy enough to ask if Cyrus had a classical education first, knowing it wouldn't be much of a riddle if he'd heard it before.
* Several variations appear in the ''VideoGame/ProfessorLayton'' series.
* ''VideoGame/SonicTheHedgehog2006'' got really ''stupid'' with this one. The Soleanna police force, intent on giving Sonic the runaround, have informed him that to progress beyond this point of the game he must ascertain which of them is the man authorized to open the door preventing him from doing so. Not only that, at least one of the five is going to lie to him. The answer ends up being [[spoiler:that the whole thing is meaningless. The captain is both the liar, and the guy who told you the terms of their little game in the first place, who just so happens to be ''standing right next to the door you need open''. He literally just has to raise his voice to get you through the door; the game was just for his own sick amusement. ''While the princess is being held prisoner'', no less]].
* ''VideoGame/{{Ib}}'' has a Room of Liars early on with six inscriptions below six different portraits telling you which tile to pull in the next room over or which portraits can be trusted. As expected, ''all'' of them are lying with one sole exception. Once you figure out the trick and solve the puzzle, your next visit to the room greets you with the sight of the truth-teller's portrait [[SpookyPainting splattered with blood and the other portraits with blood on their hands...]]

* ''VideoGame/DarkSeedII'' introduces an interesting variation. Two guards, Ik and Uk, guard a door. The player has to tell which one is which, ''and'' if it is day or night. However, there is no sun in their world, and the role of Knight and Knave changes depending if it is day or night. Unfortunately, since the game won't let the player figure it out on his own, he must ask someone else which is the Knight and Knave during day and night.
* ''[[https://rpgmaker.net/games/456/ Professor McLogic Saves the Day]]'' is built entirely on this trope: not only do you need to discern truth-tellers from liars and alternators, you also need to deal with animals whose truth-telling/lying ways are reversed by gender and rabidness, philosophers who speak only in "if-then" statements, politicians who love telling you what they ''think'' others would say instead of their actual party affiliation/honesty, creatures who tell the truth only at certain phases of the day...and that's just a small sample of the numerous variations this game manages to bring to the table.
* A sidequest in ''VideoGame/Borderlands2'', "[=BFFs=]", has four robbers in a [[MexicanStandoff Truxican Standoff]] over which of them stole the money from a heist they recently pulled off. One of them is telling the truth, and the other three are lying. You can just shoot any of them in the head to complete the quest, but if you properly figure out who took the money, you'll get a better reward. [[spoiler:It's Lee, the only one who didn't specifically accuse anyone else. Oh, and he has a box with a dollar sign on his back.]]
** Note that figuring out which one is truthful isn't required, as the culprit is one of the liars. For the record, it was probably [[spoiler:O'Cantler. He accuses one of the others of ''lying'', but not of taking the money.]]
* In ''[[Creator/ZapDramatic Sir Basil Pike Public School]]'', picking the girl's path gives you this puzzle with Duke and Luke Crabtree, who try to either guide or deter you from the tennis court. (The boy's path has a ThreePlusFiveMakeFour puzzle instead.)
* ''VideoGame/{{Avernum}}: Escape From the Pit'' references this trope with a sign in Erika's tower, but ultimately averts it:
-->One goblin tells the truth,\\
The other lies.\\
[[CuttingTheKnot Pierce them both to get the prize]].
* ''[[http://www.kongregate.com/games/rete/i-have-1-day I Have 1 Day]]'' has one puzzle in which you have to decide which one of two wizards you know for sure is telling the truth after hearing one statement from each of them. The solution is to talk to the third wizard who explained the rules of the puzzle to you -- you can't know for sure if either of the other two wizards are telling the truth from their statements, but you ''can'' be pretty sure that the wizard who told you the rules was telling the truth.
* ''[[VideoGame/DrBrain Castle of Dr. Brain]]'' has a room with three robot heads you need to choose from to help manage a programming task, but one always tells the truth, one always lies, and one alternates, and this affects how they handle programming instructions. (The liar does opposite tasks, for instance.) You don't get to ask any questions; all they do is introduce themselves. All three says they themselves work properly, but Propeller Head says that Iron Face also works properly, Iron Face says that Saucer Head never works properly, and Saucer Head says he's the only reliable head. This gives you enough clues to figure out who's who.
* The Creator/{{AGD Interactive}} remake ''[[VideoGame/KingsQuestIIRomancingTheThrone King's Quest II: Romancing the Stones]]'' used this on the stone lions guarding Hagitha's keep. However, owing to the fact that most of their audience has probably heard it before (and the graphical interface), the two lions simply tell you what the other one say if you asked if that one knows the way in.
* One puzzle in ''[[VideoGame/CubeEscape Rusty Lake: Roots]]'' requires you to figure out which one of four people are the [[TarotMotifs High Priestess]] (always tells the truth), the Devil (always lies), the Chariot (lies only once), and the Empress (tells the truth only once) from their written statements.
* The 1990s {{shareware}} game [=MasterSpy=] is built around this. To win the game, you have to start by figuring out which of the three information sources is still telling the truth, while the other two have been corrupted by TheMole and always lie. This is done by spotting contradictions, such as '''RADIO: THE SHIP TICKET CANNOT BE USED''' vs. '''TELEPHONE: THE SHIP TICKET WILL ALLOW AN AGENT TO ESCAPE''', or alternatively '''RADIO: TELEPHONES TELL LIES'''. Either of these will tell you that the third info source (Letters) must be one of the liars.
* ''VideoGame/TheCatLady'' has a standard instance of the Knights and Knaves riddle with two doors, the only variation being that the Knight and Knave are represented by a pair of gigantic [[CreepyDoll creepy dolls]].
* ''VideoGame/PaperMarioTheOrigamiKing'': One of the puzzles in the Trial of Wisdom on Diamond Island involves having to talk to three statues and decide which of them is the liar.
* ''VideoGame/DragonQuestVI'': In the fifth floor of Gardsbane Tower, the hero finds three doors and three persons. You have to talk to them to figure out which is the right door, but only one of them is telling the truth. The young man on the left claims there is nothing past his door, and the right door is on the right; the old man on the center says you will get hurt if you open his door. And the woman on the right tells the young man is telling the truth. Which of them is is truthful? Actually, the old man, since the center door leads to a spiked floor. Meanwhile, the left door leads to a treasury which is ''not'' the one the hero is looking for, and the right door leads to the Tower's real reward.
* In ''VideoGame/{{Darklands}}'' most puzzles in dwarven mines are either this or mathematical rebuses.
* In the Aeanea Spring Breeze event from ''VideoGame/FateGrandOrder'', the party (the player, Odysseus, Circe, Arjuna, Jason, and Orion) comes across three gates guarded by Mephistopeles, Shakespeare and Great Stone Statue God, all three of whom are claiming that the other two are telling lies and they should trust them instead. Circe figures out that the real liar in all of this is the sign who is telling the party to break the paradox and go onward without looking back, with it instead saying to turn back to proceed. The three gate guards still attack as she also said that they were just a sideshow, pissing them off.
* Referenced in ''VideoGame/ALinkToThePastRandomizer'', where the woodcutters may have their dialogue randomly replaced with “One of us always lies”.

[[folder:Visual Novels]]
* In the ''VisualNovel/{{Umineko|WhenTheyCry}}'' fan novel [[RPGEpisode "Witches and Woodlands,"]] the heroes are presented with this trope during their quest. Most of them already know the solution, and Battler chides [[GameMaster Beatrice]] for getting so lazy with her puzzles. Unfortunately, [[InsufferableGenius Erika]] refuses to use the standard solution, so she uses the existence of [[LanguageOfTruth red text]] to figure out which guard is the liar and which is the truth-teller. Everyone is suitably impressed... until the [=NPC=] in charge of the test reminds her that [[OutGambitted the point was to figure out which door was the safe one, and she just wasted the party's one question.]] (Bonus points for referencing the ''Film/{{Labyrinth}}'' and ''[[Webcomic/TheOrderOfTheStick Order of the Stick]]'' examples during the test.)
[[/folder]]

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* ''A God's Life'' spoofs it [[http://www.sylvanmigdal.com/agl/agl17.html here]] (last two pages).
-->'''Disembodied voice:''' The guards are politicians. One tells half-truths, the other dodges questions.
* In a ''Webcomic/BiterComics'' [[http://www.bitercomics.com/comic/deciduous-dilemma/ strip]], a two headed tree that guards the safe path out of the forest attempts to use this old riddle, although he proves to not be particularly good at it.
* In ''Webcomic/EightBitTheater'', Fighter decides working out whether or not Thief is lying is like one of these puzzles, and comes up with the following [[http://www.nuklearpower.com/2006/12/09/episode-780-brain-teaser/ sequence of words]]:
-->'''Fighter:''' So you ask one guy, doesn't matter which, what the ''other'' guy had for lunch that day. Then you ask the ''other'' guy what he ''didn't'' have for lunch. If their answers differ, then you know that ''one'' tells the truth while the ''other'' one lies.\\
'''Black Mage:''' And what if they say the same thing?\\
'''Fighter:''' Then the conspiracy goes ''straight'' to the top.\\
'''Black Mage:''' ''What'' conspiracy?\\
'''Fighter:''' I wish I knew, BM. I wish I knew.
* Invoked in [[http://www.unshelved.com/2007-3-22 this]] ''Webcomic/{{Unshelved}}'' strip. After discussing the fact that Tamara's jokes aren't funny because she has to say "just kidding", whereas Dewey is so flippant that no one realizes when he's being serious, they decide that for the rest of the shift Dewey will always say what he means and Tamara won't. Mel concludes that she's somehow ended up in a logic problem.
* ''Webcomic/{{Housepets}}'' uses the "three guard" variant [[http://www.housepetscomic.com/comic/2017/10/25/two-heads-are-better-than-three/ here]], with the added caveats that they must find out which guard answers randomly, each guard only answers with "Bo" or "Lal", and if you ask them more than two questions the puzzle resets with the roles of the guards swapped. Peanut, using his newly acquired SmartBall, [[http://www.housepetscomic.com/comic/2017/10/27/one-head-is-better-than-two/ solves it]] by asking the first two guards (the liar and the truth-teller, incidentally) [[LogicBomb a question they can't answer truthfully or falsely]], causing them to explode and leaving only the random one, which would have survived Peanut's logic bomb anyway.
* One ''Webcomic/{{Oglaf}}'' strip is titled [[https://www.oglaf.com/knightsandknaves/ "Knights and Knaves"]] and involves adventurers encountering two doors in a dungeon that offer the typical puzzle. The adventurers take the door's claim that "You may take either door" overly literally, and steal one of the doors. At their stolen home goods store, the door offers bogus deals to customers, and a salesperson warns "This door always lies."
* Webcomic/TheBestGamepiecePhotocomic: [[https://www.theduckwebcomics.com/The_Best_Gamepiece_Photocomic/5642716/ This strip]] features a character using a LogicBomb against one. The guards respond by [[spoiler:[[CuttingTheKnot just telling him the answer.]]]]

* Ricky and Steve do the "Heaven and Hell" version of this with Karl Pilkington on ''Radio/TheRickyGervaisShow.'' His answer is to pretend to be a postal worker and ask them to send God out to sign for it. Rather hilarious bit of FridgeLogic is the fact that they use the "Hell-Door guard lies, while the Heaven-Door guard tells the truth" version, meaning that their answer isn't that much better, being overly complicated. Karl being Karl, he remains convinced that ''something'' would give the liar away and that you'd need to rely on instinct to spot it even ''after'' Ricky and Steve have explained how to solve the problem with logic.
* ''WebVideo/JourneyQuest'' does this with Glorion [[spoiler:killing the truth-telling gargoyle, believing the liar, and getting annoyed by the liar contradicting him -- finally asking if he wanted to die. The liar, forced by his nature, says yes, and is thrown through the door he has convinced Glorion leads to his death]]... demonstrating its safety.
* ''Website/SCPFoundation'': [[http://www.scp-wiki.net/scp-4390 SCP-4390]], a knock-off of ''Film/{{Labyrinth}}'', features a variant on this puzzle with two Spanish-speaking brothers named Señor Honestidad and Señor Deshonestidad as one of the challenges the exploration team faces. [[spoiler:The one asking the questions bungles the question by asking them which path to go down, but their names are a dead giveaway]].

* ''WebVideo/SevenSecondRiddles'': At least one puzzle followed this plotline, involving the riddle's protagonist having to escape a cave where two guards stood at the exits- one liar, one truth teller.

* This is one of the many [[http://web.archive.org/web/20100914155050/http://powerpuff.wikia.com/wiki/Him_Diddle_Riddle/The_Ms._Keane_Puzzle_Explained puzzles]] presented to ''WesternAnimation/ThePowerpuffGirls1998'' by HIM in the episode "Him Diddle Riddle." Blossom uses the "If I asked the other person..." variant by asking "which person would ''the other Ms. Keane'' say is the real one?". Blossom then tries to explain the whole thing to Bubbles and Buttercup, who are hopelessly lost in trying to figure out Blossom's logic. In spite of not getting it, HIM concedes that Blossom chose correctly, and lets Ms. Keane go.
* Also subverted in an episode of ''WesternAnimation/SamuraiJack''. A two-headed creature poses this riddle to Jack, claiming that one of his heads is magic, and if he chooses to be swallowed by it, he will be granted a wish, while if he is swallowed by the other head he will simply be eaten. One head always lies, and the other always tells the truth. Jack solves the riddle using the "If I asked the other one which was correct..." solution, [[spoiler: but it turns out that it was all just a trick by the creature to get idiots to willingly feed themselves to it. [[SnapBack We're not shown how Jack escaped this situation]], but given Jack is [[JustEatHim still alive when he arrives in their stomach]], he probably cut his way out.]]

* ''WesternAnimation/KingOfTheHill'': In "A Beer Can Named Desire", Bill Dauterive returns to his family's estate in New Orleans, where three Dauterive widows are all lusting after him, [[KissingCousins but one of whom is his cousin by blood]]. Despite Peggy's attempts at telling Bill to avoid them, he decides to go after them. Things get intense when they all they try to sleep with Bill, with each accusing one of the others of being the cousin before they begin brawling with one another. That's when Bill's male cousin, [[AmbiguouslyGay Gilbert]], [[LightswitchSurprise enters]] and reveals that Violetta was the cousin, [[ThrowTheDogABone and we later learn Bill slept with the two non-cousin widows, after all]].

* A variation is made in ''Anime/GhostInTheShellStandAloneComplex'' where the endlessly curious Tachikoma's steals the hardware for a sniping assistance device by using the statement as a logic bomb.
* ''Anime/PhiBrainPuzzleOfGod'' had a more complex variant. The main was set upon 7 Dwarves with 7 apples, color coded. Each would say something to help determine which Dwarves were Lying or telling the truth, and which apples (the goal) were "delicious" (the right ones). The Puzzle itself was flawed in that he was never told how many "delicious" apples there were.

* A Mathnet comic (from ''Series/SquareOneTV'') included in a tie-in magazine issue of Series/ThreeTwoOneContact involved this puzzle. Kate Monday and George Frankly had to find out which of two identical twins were stealing birds from pet stores. One revealed that he always told the truth and his brother always lied - leaving the two detectives to figure out who was the thief. This particular Knights and Knaves puzzle was a variation on the traditional format; no limit on questions allowed was specified. The solution given was to ask the brothers a trick question like "Are you a parrot?" It was reasoned that the brother who always lied would say "yes" and the always truthful brother would say "no".

* Parodied in ''Fanfic/TheDarkerKnight'', where Riddler and Riddlercousin attempt to claim they have this dynamic going. Batcousin accuses them of both lying, and then they apologise and randomly die.

* In ''The Man Who Counted'', Beremiz is presented with an arguably more difficult variation. He is presented with five slaves, and he has to find out their respective eye colors (he can't [[DungeonBypass see]] their eyes because they are covered by burqas). The black-eyed two always tell the truth, and the blue-eyed three always lie --he is allowed three questions, no more than one per slave. [[spoiler:Beremiz asks the first one her eye colour, knowing her answer to be "My eyes are black" in advance, and he asks the second one for the first's ExactWords[[note]]It helps that the first slave's answer was in a foreign language[[/note]]. She answers "She said her eyes are blue". Then he asks the third one for the eye colour of both of them. She says that the first's eyes are black, and that the second's are blue. Since Beremiz could confirm that the second slave had lied, he marked this one as truthful, and so he submitted his answer: the first and third slaves have black eyes, while the second, the fourth and the fifth's are blue]].
* The short story ''Literature/HowKazirWonHisWife'' by Creator/RaymondSmullyan involves various more complicated variations on the puzzle, while the framing story is set on an island where the normal version has occurred.
* Spoofed in the ''Literature/{{Discworld}}'' novel ''Literature/LordsAndLadies''. To pass the time on their trip to Lancre, Ponder Stibbons mentions this puzzle to Ridcully and Casanunda. Much to Ponder's annoyance, Casanunda insists that the "logical" solution is to wrestle a weapon from one of the guards and force him at swordpoint to show them which door leads to safety. And inform him that he is going in first, just in case he tries any funny business.

* In the backstory ''Literature/TheGoneAwayWorld'' by Nick Harkaway, Mr. Soames is confronted by three anthropophagous witches who offer to give him directions using the standard Knights and Knaves setup. Being a logician, he takes them up on the offer. [[spoiler: The whole thing is a trap, which is why Mr. Soames is dead in the main story.]]
* A variation in one of the junior ''TabletopGame/{{Clue}}'' books, where one of [[AbsentMindedProfessor Professor Plum]]'s inventions causes [[GrandeDame Mrs. Peacock]] to [[CloningBlues get cloned]]. The catch is that her clones are aware they're clones, violently homicidal (well, moreso than usual), and uncontrollable liars, but none of the other guests nor Mr. Boddy himself realize this until the last page. They keep asking "Which of you is the real Mrs. Peacock?", which only leads to the inevitable answer of "I am!" from all of the Peacocks present. The book asks the reader to supply the answer to find the real (presumably truth-telling) Mrs. Peacock--the solution being simply to ask a purely factual question such as "What is two plus two?" and presumably dispose of the clones who started spouting mathematical nonsense.

* In ''Literature/TheHauntingOfDrearcliffGrangeSchool'', a teacher poses the puzzle to her class, but neglects to include the "only one question" restraint. The class's GentleGiant says that she would find out which was the truth-teller by thumping both of them and asking "Who wants me to do that again?", and the rest of the students agree that this makes as much sense as the answer in the textbook.
* ''Literature/{{Hilda}}'': Hilda faces a riddle like this in ''Hilda and the Hidden People'', with two water spirits as the liar and truth-teller respectively. She has to figure out which of two caves is the one the Elf Prime Minister resides in, with the other supposedly housing a flesh-eating troll, by asking the two water spirits only a single question.

* The ''Series/DoctorWho'' serial "[[Recap/DoctorWhoS13E3PyramidsOfMars Pyramids of Mars]]" features this as one of several puzzles the Doctor had to solve to enter the titular structure. This incident is an example of solution #2, asking the one guard about what the other guard would have said. Why an ancient Martian pyramid imprisoning a SufficientlyAdvancedAlien was protected only by ''[[SolveTheSoupCans logic puzzles]]'' is unknown. The Doctor, being the clever bastard that he is, figures it out in about 15 seconds. According to the DVD production notes subtitles, Creator/PhilipHinchcliffe got it from Franz Kafka's ''The Castle'', although this cannot be confirmed.
* Straight example in the math-and-logic EdutainmentShow ''Series/SquareOneTV'', with the three-person variant. The alternating character, when asked who he was, said he was the knave, which neither the knight nor the knave would say. Then the knave claimed to be the alternator, which the hero had already identified, leaving the last person to be the knight. Of course, this is a little contrived, as ''both'' the Knave and the alternating character could claim to be the Knight, in which case you'd be stuffed, since all three would be claiming the same thing.

-->'''Tony:''' All right, all right. Wait, wait! I have a question! What is the point in having a door that has a horrible death behind it? Huh? (''picks up frog'')\\

'''Frog:''' Don't touch me there, only my girlfriend touches me there! (Tony throws the frog through one of the doors) WHOA! (''Tony slams the door, there's a large explosion and fireball'')\\

* Discussed in the Canadian kids' show ''Series/RadioActive'', where the students are assigned the problem in class but the proper answer is never figured out.
* Is analysed as one of the puzzles on Dara O'Briain's show ''School Of Hard Sums'' with the catch that you can only ask one question. The answer given in the show is [[spoiler: "Will the other person claim their door is the correct one?"]] which always results in [[spoiler: a lie]].

* There was a brain teaser in a ''Series/DoctorWho'' annual about two captured soldiers (astronauts?) who were told that they could make one statement, If their statement was judged as true they would die by lethal injection, if their statement was judged as false they would die by hanging. They managed to make a single statement that meant the judge had to let them go. The answer? [[spoiler:They make the statement "I will die by hanging" if they hang them that makes the statement true, which should mean the die by lethal injection, which would then make the statement false, which would mean they should die by hanging and so on.]]
** ''VideoGame/ZorkZero'' features a similar riddle; however, the LogicBomb only works once and if you are stupid enough to try again, the riddle-makers have gotten wise to this loophole and made an ObviousRulePatch.
* ''Series/LawAndOrderCriminalIntent'': Goren sets this puzzle for his psychiatrist in "The Consoler". His version has a disguised angel guarding the doorway to Heaven, and a disguised demon guarding the doorway to Hell. The Angel tells the truth and the demon lies.
* ''Series/TheMole'': The Belgian series' 4th season had a challenge that gave one of its 3 finalists the opportunity to learn with 100% certainty who the Mole was. They had to choose one of two rooms to enter and then ask the man inside that room a single yes-or-no question, but one of these two men would tell them the truth and the other man would lie and they wouldn't know which man was which. [[spoiler:Gilles, the winner of that challenge, figured out the right question to ask -- but since ''he'' was the Mole, it was done just for show.]]
* ''Series/{{Harmonquest}}'': The party runs into this puzzle played completely straight. Spencer barely has enough time to finish explaining the concept before Jeff blurts out the solution, obviously well acquainted with this trope.
* ''Series/MidsomerMurders'': In "The Death of the Small Coppers", DS Winter, who hates riddles, is captured by the killer who places him in a DeathTrap and offers to let him live if he can solve this puzzle in five minutes. Ironically, one of the suspects had offered to tell him the answer to this earlier in the episode.

* In a 2023 ''ComicStrip/{{Popeye}}'' strip, Popeye and Olive Oyl encounter a pair of these. Olive's suggestion is that Popeye punch them both and see which one says it doesn't hurt. Instead, Popeye asks them both how they're doing. One has a litany of complaints, the other just says "I'm fine". Popeye chooses the first one's gate, explaining to Olive "Think about what the last few years were like, and tell me if ya'd believe anyone sayin' they is 'fine'."

* Parodied in the first episode of ''Radio/JohnFinnemoresSouvenirProgramme'' in [[https://www.youtube.com/watch?v=02gfh-h6mTQ this sketch.]]

* Referenced in one episode of ''Radio/TheNewsQuiz'', when Mile Jupp suggests there are two UsefulNotes/{{Theresa May}}s: "One always lies, one always tells the truth. One guards the road to prosperity, the other to stagnation. And you can only ask one of them one question."

* ''TabletopGame/PerplexCity'' has a version with seven speakers, at least three of whom are knights and three of whom are knaves.

* ''TabletopGame/DungeonsAndDragons'', Module I3 ''Pharaoh''. Inside the tomb of Amun-re the {{PC}}s can encounter an androshpinx who offers to play a RiddleMeThis game with them. If they can answer one of his riddles he will answer a question from them about the tomb. Riddles he can ask include one of these puzzles. People who live on the west side of Bindon always tell the truth, people who live on the east side of Bindon always lie. However, people who live on one side of town can sometimes be found wandering around the other side. If you're in Bindon, how can you find out which side of town you're currently on by asking someone? Answer: ask a passerby [[spoiler:"Do you live here?" If you're on the west side the answer will always be "yes", on the east side the answer will always be "no"]]. Then just hope the person you ask isn't a visitor from out of town...
* ''TabletopGame/{{Pathfinder}}'': Subverted in ''Gardens of Gallowspire'', the fourth installment of the ''Tyrant's Grasp'' adventure path. The players encounter two wraiths in the depths of Gallowspire's catacombs, who tell them in rhyme that one of them always lies and the other always tells the truth, and that if they can determine which one is which they must turn away from the liar and ask the truth-sayer for the correct path. They then proceed to say a number of cryptic, confusing statements when interacted with. This is purely a ruse intended to get the [=PCs=] to drop their guard and turn their back on one wraith, after which they both attack. Their cryptic comments are simply so much [[IceCreamKoan profound-sounding nonsense]].

* ''Film/{{Labyrinth}}'': The LicensedGame for the Commodore 64 includes the scene as described in the Film folder; but as the engine was too limited to let you ask specific questions, the solution is different. The player must open each door and see which path has the sign saying "[[NeonSignHideout To the Castle]]" and which says "[[ThisWayToCertainDeath To Certain Death]]." The real danger is assuming that [[OutGambitted something so obvious must be a trick]] and falling to your doom.
* ''VideoGame/FinalFantasyVI'': The DungeonTown of Zozo is part of a Knights and Knaves puzzle where ''everyone'' in town is a Knave. There are people there that don't lie, but none of them are native to the town, and they don't contribute to the puzzle. The Knaves all tell you what time it is, and each statement is false. By process of elimination, you can find out the correct time, and use a clock late in the dungeon to access the {{Chainsaw|Good}} for Edgar.

* ''VideoGame/{{Ultima}}'' features a two-headed horse called the [[Literature/DoctorDolittle Pushmi-Pullyu]], whose heads are a Knight and a Knave. The puzzle is substantially simplified to fit the interface -- however you put the question to it, he answers by telling you what his other head would say. And since his explanation of his nature is the same whichever head is speaking, there is something of a flaw in the setup. Not that it really matters anyway, as he tells you only which of two routes is less dangerous, but by the time the player reaches him, neither route is particularly dangerous, and the MoneySpider enemies actually make the "wrong" answer more attractive.

* A variation of this problem appears as a puzzle in ''VideoGame/EscapeFromMonkeyIsland'', where Guybrush needs to find hidden treasure with the help of two parrots named Huggyn and Kyssin, who are enchanted by voodoo magic to always tell the truth and lie, respectively. The catch with this variation is that you're asking for directions where there are at least three choices at each intersection. Also, the parrots are identical and fly up and off the screen, then come back after answering a question, so you can no longer tell which one tells the truth. [[spoiler:The trick is to intoxicate one of the parrots with caffeine or alcohol, which produces an obvious change in the bird's appearance -- don't worry, it wears off as soon as you finish the puzzle.]]
* This puzzle appears in ''VideoGame/ZorkZero''. The catch here is that which one lies and which one tells the truth is randomized each time you enter the room, and while in the room, ''you're not allowed to save.''
* A valley near Esthar in ''VideoGame/FinalFantasyVIII'' contains a multitude of talking rocks that put Squall's wits to task with this riddle... in theory. In practice they're pretty much ''all'' full of it, and it's easiest to solve the puzzle simply by wandering around pressing the X button until you hit the right spot.

* ''Website/{{Neopets}}'' does this too in the Tale of Woe (an old Plot). There was this Mutant Hissi, which you had to question. (For those who don't know, a Mutant Hissi has two heads.) The solution is to stab one of the heads, and then ask: "Did it hurt?" If the head answers no, it lies.

* In the ''VisualNovel/{{Umineko|WhenTheyCry}}'' fan novel [[RPGEpisode "Witches and Woodlands,"]] the heroes are presented with this trope during their quest. Most of them already know the solution, and Battler chides [[GameMaster Beatrice]] for getting so lazy with her puzzles. Unfortunately, [[InsufferableGenius Erika]] refuses to use the standard solution, so she uses the existence of [[LanguageOfTruth red text]] to figure out which guard is the liar and which is the truth-teller. Everyone is suitably impressed... until the [=NPC=] in charge of the test reminds her that [[OutGambitted the point was to figure out which door was the safe one, and she just wasted the party's one question.]] (Bonus points for referencing the ''Film/{{Labyrinth}}'' and ''[[Webcomic/TheOrderOfTheStick Order of the Stick]]'' examples during the test.)

-->'''[[HeroicComedicSociopath Pokey:]]''' ''[hacking at one of the doors with a sword]'' Does this hurt?\\

* ''Webcomic/{{XKCD}}'' also has fun with it [[http://xkcd.com/c246.html here,]] as quoted above. The AltText takes it further: "And the whole setup is just a trap to capture escaping logicians. None of the doors actually lead out." Also referenced [[http://xkcd.com/1132/ here]] in the AltText.
* In Episode 327 of ''Webcomic/TheOrderOfTheStick'', this is the [[http://www.giantitp.com/comics/oots0327.html Test of the Mind]] the Order goes through to get to the Oracle of Sunken Valley (which prompts Roy to remark "that's the last nail in the coffin for the hope that these Tests would be even remotely original"). Haley solves it by [[CuttingTheKnot shooting one of the guards]], then noting that the guard she shot is screaming "you shot me!" while the other guard insists "she totally didn't shoot you". The next time Haley passes through, the guards remember her and hastily direct her to the correct path before she can do anything. Haley doesn't understand why, because the Oracle's [[LaserGuidedAmnesia memory charm]] means nobody remembers anything that happens in the valley ''except'' for the answer he gives them.

* ''Webcomic/{{Girly}}'' features what probably is the most nonsense solution for the problem in the strip "[[http://go-girly.com/go/347 Knights and Knaves]]". Basically, the right question is "Are you wearing a sombrero?" Of course, given the setup of that particular instance ("the correct path lies with the one who tells the truth"), ''any'' question you already know the answer to will do.
* Parodied in ''Webcomic/PartiallyClips'': [[http://partiallyclips.com/comic/paradox-dragon/ here]]. No solution is offered or expected, but for the record, [[spoiler: the puzzle is unsolvable, as the premise is false - both the second and third heads contradicted themselves, something which only the alternator would do]].

* On ''Webcomic/BobAndGeorge'', when Mega Man gets to [[MesACrowd Gemini Man]], one of them claims that they tell [[RiddleMeThis riddles]] (they don't) and begins with this one. When the other tries to protest, the first merely passes off everything as a lie. Mega Man just stands there, reflecting on what Wily bots have been reduced to.

--> '''Disembodied voice:''' The guards are politicians. One tells half-truths, the other dodges questions.

* Subverted in ''Anime/YuGiOh'' During the Duelist Kingdom arc, the Paradox Brothers confront Yugi and Jounouchi/Joey with this puzzle. Joey thinks he's solved the riddle, seeing that he's heard it before, but Yugi correctly guesses that the brothers' description of the puzzle is in fact part of it, and that ''both'' the brothers are lying about the whole puzzle (they both say that one ''always'' lies and one ''always'' tells the truth, which is impossible because someone who ''always'' lies would be unable to give an honest description of the puzzle, and thus could ''never'' agree with someone who always tells the truth), and outwits them his own way. They're cheaters, anyway. Whenever a person asks his question and chooses a door, they always claim the opposite door is the right one. Yugi [[BeatThemAtTheirOwnGame tricks them]] by making them think he's choosing one door via ExactWords, waiting for their answer, and revealing he chose the other one. [[spoiler:[[ShaggyDogStory Both doors lead to the exact same place anyway]]]].

[[folder: Newspaper Comics]]

* Subverted in the MiniSeries ''Series/TheTenthKingdom''. Two doors to safety or death are guarded by a talking frog who offers one question, but claims to always lie (which would make it unsolvable as a logic problem since the rules themselves are in doubt). By now the father of the protagonist Virginia has had it with this kind of puzzle.

* This is one of the many [[http://web.archive.org/web/20100914155050/http://powerpuff.wikia.com/wiki/Him_Diddle_Riddle/The_Ms._Keane_Puzzle_Explained puzzles]] presented to ''WesternAnimation/ThePowerpuffGirls1998'' by HiIMin the episode "Him Diddle Riddle." Blossom uses the "If I asked the other person..." variant by asking "which person would ''the other Ms. Keane'' say is the real one?". Blossom then tries to explain the whole thing to Bubbles and Buttercup, who are hopelessly lost in trying to figure out Blossom's logic. In spite of not getting it, HIM concedes that Blossom chose correctly, and lets Ms. Keane go.
* Also subverted in an episode of ''WesternAnimation/SamuraiJack''. A two-headed creature poses this riddle to Jack, claiming that one of his heads is magic, and if he chooses to be swallowed by it, he will be granted a wish, while if he is swallowed by the other head he will simply be eaten. One head always lies, and the other always tells the truth. Jack solves the riddle using the "If I asked the other one which was correct..." solution, [[spoiler: but it turns out that it was all just a trick by the creature to get idiots to willingly feed themselves to it. [[SnapBack We're not shown how Jack escaped this situation]], but given Jack is [[JustEatHim still alive when he arrives in their stomach]], he probably cut his way out.]]

* Also subverted in an episode of ''WesternAnimation/SamuraiJack''. A two-headed creature poses this riddle to Jack, claiming that one of his heads is magic, and if he chooses to be swallowed by it, he will be granted a wish, while if he is swallowed by the other head he will simply be eaten. One head always lies, and the other always tells the truth. Jack solves the riddle using the "If I asked the other one which was correct..." solution, [[spoiler: but it turns out that it was all just a trick by the creature to get idiots to willingly feed themselves to it. Very likely, Jack cut his way out afterwards]].

* ''Wiki/SCPFoundation'': [[http://www.scp-wiki.net/scp-4390 SCP-4390]], a knock-off of ''Film/{{Labyrinth}}'', features a variant on this puzzle with two Spanish-speaking brothers named Señor Honestidad and Señor Deshonestidad as one of the challenges the exploration team faces. [[spoiler:The one asking the questions bungles the question by asking them which path to go down, but their names are a dead giveaway]].

For the record, the most common solution to the above scenario is to ask one of the guards, "If I asked you if the door you're guarding leads to where I want to go, would you say 'yes'?" If the guard says "yes", then you go through his door; if he says "no," you go through the other guard's door. This is because his answer to this question doesn't depend on which guard he is. Say he says yes to the question. If he's telling the truth, then he ''would'' say that the door leads to where you're going, and thus, the door will lead to where you're going. If he's lying, then he'll have to lie about whether he'd say Yes to the question (which, in this case, he would ''not'' say yes if asked if the door led to where you're going, and would in fact say no) and, thus, is forced to give the correct answer to where the door goes. Of course, this requires that both guards know where you are going, and that neither of them considers "Your doom" a place. And interesting property of this solution, as opposed to the "other guard" solution, is that it even works if one guard is missing.

* In ''Machinima/Supermarioglitchy4sSuperMario64Bloopers'', [=SMG4=] and Mario encounter two Piranha Plants in [=SMG3=]'s dungeon filling this role. Naturally, [=SMG4=] solves the riddle with the opposite answer solution, while Bowser just sets them both on fire and enters the wrong door.

* This is one of the many [[http://web.archive.org/web/20100914155050/http://powerpuff.wikia.com/wiki/Him_Diddle_Riddle/The_Ms._Keane_Puzzle_Explained puzzles]] presented to ''WesternAnimation/ThePowerpuffGirls'' by Him in the episode "Him Diddle Riddle." Blossom uses the "If I asked the other person..." variant by asking "which person would ''the other Ms. Keane'' say is the real one?". Blossom then tries to explain the whole thing to Bubbles and Buttercup, who are hopelessly lost in trying to figure out Blossom's logic. In spite of not getting it, Him concedes that Blossom chose correctly, and lets Ms. Keane go.

* As the trope description mentions, Raymond Smullyan [[TropeCodifier popularized]] this trope with his many books full of this kind of puzzle, including but not limited to ''What is the Name of This Book?'', ''The Lady or the Tiger?'', and ''Alice in Puzzle-land''. ''Alice in Puzzle-land'' in particular is noteworthy for having a conversation between Alice and the King of Hearts that lampshades/[[DiscussedTrope discusses]] how this sort of puzzle has become so well-known that some people assume that the most famous examples of it are the ''[[SmallReferencePools only]]'' possible variants of it; when the King begins to talk about knight and knave puzzles, Alice interrupts him to say that she already knows these puzzles, whereupon the King gets annoyed and retorts that there are countless possible puzzles about truthtellers and liars and that her knowing some of these puzzles doesn't necessarily mean that she'll also know the ones he wants to tell.

* ''WesternAnimation/KingOfTheHill'': In "A Beer Can Named Desire", Bill Dauterive returns to his family's estate in New Orleans, where three Dauterive widows are all lusting after him, but one of whom is his cousin by blood. Despite Peggy's attempts at telling Bill to avoid them, he decides to go after them. Things get intense when they all they try to sleep with Bill, with each accusing one of the others of being the cousin before they begin brawling with one another. That's when Bill's male cousin, [[AmbiguouslyGay Gilbert]], [[LightswitchSurprise enters]] and reveals that Violetta was the cousin, [[ThrowTheDogABone and we later learn Bill slept with the two non-cousin widows, after all]].

* Appears in ''Series/TheLegendOfWilliamTell'' when Kalem is trying to teach Will to think about things. His companions, including his SmartGuy, have already gone through one of the doors, but they slam in his face and he has to logic his way through.