Spotting the Thread in Anime & Manga.
- Done in Alive: The Final Evolution, where one of Big Bad Katsumata's Comrades was a female Body Surfer named Han sent to infiltrate the American military by entering the body of one of James McPherson's subordinates to locate the Mineral MacGuffin "the heart of Akuro". Despite possessing the memories of his host body, Han is eventually shot in the heart by McPherson when he notices that his subordinate keeps his nails unusually clean and manicured.
- Attack on Titan:
- Armin can even identify the scratches and dings on Marco Bott's 3D Maneuver Gear when he sees Annie Leonhart present it for inspection in place of their own gear, to prevent anyone from realizing that she'd used her own gear to kill "Sawney" and "Bean", the captured Titans being used as test subjects.
- Reiner and Bertolt had a Conveniently Unverifiable Cover Story and avoided associating with their co-conspirator, to avoid any suspicion. But one mistake leads to them being suspected — their falsified documents listed them all as coming from the same region.
- The other bit of damning info came when Armin remembered that during the 57th expedition, Reiner had been overtly interested in figuring out where Eren was; and, after a run-in with the Female Titan, she had changed course.
- While examining a crate full of canned goods, Ymir complains about it being Herring, a food they don't particularly like. Their companion is shocked, because the label is in another language and therefore shouldn't be possible to read.
- Much later in the manga Eren sneaks into Marley disguised as a wounded soldier, but puts his Eldian armband on the wrong arm. Subverted in that he's never found out; the one person to notice is Naïve Newcomer Falco, who assumes that Eren's suffering from Shell-Shock and puts it on the right arm for him. Too late, Falco spots a second thread; if "Kruger" met Reiner more than four years ago, it was probably while Reiner was infiltrating the Island of Paradis, meaning that the "friend" is an Eldian and an enemy.
- Call of the Night: Yamori manages to deduce that no one is stalking Arisa through a few subtle details, such as the quality of the pictures being too high for a peeping tom to have taken them during a brief window of opportunity, all the pictures being taken when Arisa was alone after the maid café had already closed, and a few of them being taken at angles the culprit couldn't have possibly used since they were taken in places they couldn't access, such as the locked balcony outside the dressing room. But more importantly, Arisa never took any Panty Shots, something which absolutely no stalker would ever pass up on.Yamori: If I don't get to be a vampire, maybe I'll be a detective when I grow up.
- Claymore: Raki is told that a Claymore is looking for him and is in the nearby forest. When they talk Raki points out, correctly, that Claymores never refer to themselves as Claymoresnote . The Reveal is that it was a Yoma impersonating a Claymore to take him hostage in order to draw Clare out and kill her.
- Crossplay Love: Otaku x Punk: Hanae's friend Shimazaki goes to Cafe Roman, where Hanae works as his female alter ego "Hana", and notices that "she" prepares his glass of water exactly the way he likes it, despite supposedly never having met him before. He confronts Hanae with his suspicions the next day at school.
- Doraemon: Nobita and the Steel Troops has a hostile robot army from Planet Mechatopia targeting earth, but thanks to Doraemon and Nobita discovering their plans, they managed to trick the robots into entering the Mirror World via a Portal Pool - which looks exactly like the real world, but is completely empty and devoid of all life. The robot army ends up destroying Tokyo, Hong Kong, New York, Paris and London, and finds no humans in the ruins, dead or alive, much to their astonishment. Until the robot's leader decide to observe the Earth on radar again and suddenly realize Japan was flipped from left to right, realizing they've been tricked in attacking a blank world.
- In Fairy Tail, Mest claims to be a disciple of Mystogan, a rather mysterious S-Class mage for the eponymous guild. Unfortunately, there's one problem with this- Mystogan puts the rest of the guild besides its master Makarov to sleep whenever he reports in for a job, so no one interacts with him. Pantherlily, who knows Mystogan personally, sees through the lie.
- Twice in Fullmetal Alchemist:
- The first time is where Maes Hughes catches out the shape-shifter Envy because he forgot a mole when he took the appearance of Maria Ross.
- The second time is where Riza catches Envy out again when he took the appearance of Roy Mustang, claiming that they were on a First-Name Basis when alone, but then admitting that she lied when he panicked - played with in this case, in that she fakes this trope in order to expose him.
- This has gotten Duke Togo in trouble a few times in Golgo 13. People who are familiar with the criminal underworld, the military, or other highly-violent environments can tell from Duke's eyes, gestures, and stance that he's extremely hardened to violence and familiar with conflict; while this doesn't immediately tell them he's a professional assassin, it does weaken any attempt he makes to pretend he's an ordinary bystander.
- Great Teacher Onizuka: Kikuchi and Urumi notice some inconsistencies in the Frame-Up Miyabi's gang did with Onizuka and the class trip money, like having a typed note from Fujiyoshi despite his family being too poor to afford a computer, and realizing that the photos were taken in the nurse's office at their own school.
- Hetalia: Axis Powers:
- England runs afoul this trope in the Can't Escape from Italy strips. His Italian disguise is eventually perfected with the help of a spy, right down to taping a curl to the side of his head, but Germany sniffs him out when England stands posturing instead of hitting on the attractive women who pass by.
- Germany himself is outed by France when he starts mashing his potatoes up instead of slicing them.
- In Hunter × Hunter, the group sees a human couple being attacked by a Shapeshifter. However, this turns out to be a Secret Test of Character that's part of the Hunter Exams.
- Kurapika notices a "thread" that was put there on purpose: the woman has (fake) tattoos that indicate a Vow of Celibacy, despite her supposedly being married.
- Gon, meanwhile, notices that the "monster" whom he's pursuing actually switches out with a different member of their species partway through the chase—this surprises and amuses them, since humans can never tell them apart.
- This is removed in the 2011 adaptation for some reason but in the manga and 1999 anime, Leorio notices and points out the needle mark on the Kiriko hunting him down, revealing it's the "husband" that he treated in the broken cabin.
- In chapter 42 of Inside Mari, Isao delivers the Wham Line "Let's lie down here together again sometime" when describing what Mari had told Yori in the nurse's room. The problem is Yori never mentioned that Mari said that to her. It's one of the most concrete signs that this isn't really a bodyswap manga.
- In Episode Ryuu, one of the spinoffs of Is It Wrong to Try to Pick Up Girls in a Dungeon?, Ryuu encounters two men (bodyguards to the arc villain) who are supposedly the infamous bounty hunter and assassin Faust and Rollo (also known as the Black Fist and Black Cat). When a fight breaks out, Ryuu points out that the real Faust and Rollo worked alone rather than as a pair, they are Level 4 (the same as Ryuu herself) rather than the Level 3 she estimates these two men as, "Faust" and "Rollo" are their real names rather than codenames, they are female rather than male (full names "Lunoire Faust" and "Chloe Rollo"), and Ryuu knows both of them personally.
- JoJo's Bizarre Adventure:
- Stardust Crusaders:
- Done hilariously when the gang books passage on Captain Dragon/Tenille's ship. Jotaro, after being insulted by the captain for smoking on his ship, accuses him of being a Stand-User instead of the stow-away Anne, who had up to that point been suspicious in her own right, and explains it away as a reaction in their nose when they smell cigarette smoke. Cue the Crusaders and Dragon/Tenille putting their hands to their noses while Anne just looks baffled.
- Later on, when crossing the desert, the group is nearly fried by Arabia Fats' Stand, The Sun, and take shelter in a small crevice dug by Star Platinum. After a long while of sitting and watching, the group one by one notices a ridiculously stupid error on Arabia Fats' part (an improper mirroring of a nearby rock) and burst out laughing at the idiocy (including the normally stoic Jotaro Kujo) before Star Platinum takes him out.
- Diamond is Unbreakable: Yoshikage Kira is subjected to this on two occasions, after some of his lies don't pass muster. First is when he is injured, obviously stares at Crazy Diamond fixing up Jotaro, and immediately asks Josuke to fix him too despite him posing as a normal civilian ignorant of Stands, when only a Stand user would figure that sort of thing out that fast. The second is when Hayato deduces his identity since Kira is doing various things that Hayato's actual father wouldn't be doing, like practicing writing his own name.
- Kira gets in on the other side of this once during the story too. Around the time that he had tamed Stray Cat and put it up in the attic, Hayato's surveillance led him to suspect the imposter posing as his father had a secret, so he waits for Kira to leave, thinking that Hayato was at school, to investigate. However, on his way to his new place of work, Kira notices some schoolchildren run past wearing their yellow hats and recalls that Hayato's was still hanging on a coat rack, so he's immediately suspicious and returns home quickly. Hayato narrowly escapes being found in the attic with Stray Cat, which also affords him the opportunity to absolutely confirm that the man is not really his father.
- Stardust Crusaders:
- In Miss Kuroitsu from the Monster Development Department, Wolf Bete is able to snap out of the effects of Purple Mirror's Lotus-Eater Machine ability through this. During the image of Wolf Bete's desires, one image reflects Wolf's inner feelings for creator/co-worker Kuroitsu. However, the Kuroitsu in the fantasy uses female honorifics when referring to Wolf Bete, whereas the real Kuroitsu knows full well that Wolf Bete is actually a male monster in a female body and thus would use male honorifics instead.
- The Lupin III franchise has Lupin calling Zenigata "Tot-san" ("Pops" or "Old Man" in English dubs). In the Lupin III vs. Detective Conan Made-for-TV Movie, Zenigata identifies the disguised Lupin when Lupin calls him by his nickname.
- Mobile Suit Gundam 0080: War in the Pocket: A group of Zeon soldiers sneaks into a space colony undergoing repairs in order to sabotage the development of a new Gundam. They actually have a very good cover story, and initially make it past security with little problem. But at one point, the rookie on the team, making small talk, remarks on how much he enjoyed the snow during Christmas in Australia. The guards get suspicious because Australia is in the midst of summer during Christmastime, and this slip-up results in quite a lot of trouble for the group.
- In Monster, Tenma is initially suspicious with two "friendly" helpers being accomplices of Johan and has his suspicions confirmed when one of them refers to him as "doctor" — something he never told them about.
- My Girlfriend Gives Me Goosebumps!: When getting a call from Rinko about his relationship with Kisaki, Haruka notices that Rinko changed how she refers to Kisaki, overreacts to being called by her first name and is asking questions for the sake of someone else. He deduces that Kisaki is listening to the call.
- In one Mysterious Joker chapter, a kid detective tries to help a pair of siblings open a special safe to claim their deceased father's inheritance. Near the end, the detective reveals that the siblings are actually thieves who tied up the real family and assumed their identities in order to trick him into opening the safe so they could steal its contents. He claims to have realized this upon noticing that despite supposedly being trained musicians, none of the siblings had calluses on their hands.
- Naruto:
- Sasuke recognizes a Naruto impostor because he doesn't have a cut on his cheek (Naruto received it before they entered the Forest of Death.), and also because the impostor is left-handed while Naruto is right-handed. After this incident, the team decides to have a secret password, so if they split up and someone comes back, they can confirm their identity via the password. Naruto promptly is separated from the group, rejoins them, and recites the password correctly. Sasuke promptly attacks. The real point of the password was to see if a Naruto impostor could recite it correctly- the real Naruto would never remember the intentionally long and complicated password, especially on his first try.
- Early in the series, Kohonamaru is spotted trying to trail Naruto, as he is holding his fence-colored camouflage in the wrong direction.
- Much later on, Sakura recognizes that Neji is being impersonated by a White Zetsu, because the impostor fails to realize that Tonton is a pig.
- Negima! Magister Negi Magi:
- The Takamichi illusion during the Bad Future Rescue Arc.
- Also done humorously, when Negi realizes that the Shizuna-sensei he's speaking to is an impostor because of a Marshmallow Hell. Turns out that the impostor (Asakura) didn't quite measure up to Shizuna's bust size.
- In the Alabasta arc in One Piece, the Straw Hats agree on a secret sign to distinguish each other if the shape shifter Mr 2/Bon Clay assumes their shape. We are shown them wearing a bandage on their arm, but the real sign is the black X drawn on the arm under the bandage, which Mr 2/Bon Clay misses when he pretends to be Usopp.
- Sometimes in Pokémon: The Series, Team Rocket gives themselves away, in spite of their Paper-Thin Disguise. This ranges from either saying something related to the twerps that only they would know (given how long they've been pursuing them), or something triggers their desire to spout out their catchphrase, causing them to blow their cover when they otherwise would have gotten away scot-free.
- In Sailor Moon R DiC dub, one of the Monsters of the Week disguise themselves as Chibi-Usa's mom and calls to her using the name Small Lady. Chibi-Usa is at first fooled, happy to see her momma again, and runs to hug her. She then suddenly stops and asked the monster who they were. When the monster replies that she was her mother, Chibi-Usa say she's lying because her mother never calls her Small Lady, her royal title. In the original Japanese the monster calls her Rabbit (which is what the Dark Moon minions had been calling her), because Small Lady is part of her actual name: Usagi Small Lady Serenity.
- In Sakura Hime: The Legend of Princess Sakura, Aoba realizes that that he is being seduced by Rurijo instead of Sakura because she had lit incense, which Sakura herself hates. In addition, her scent aside from that was off; since Aoba can transform into a wolf, his sense of smell is very sensitive.
- Soul Eater: Death the Kid confronts Free in a room under the DWMA and is initially having trouble against him because none of his bullets seem to hurt him apparently due to his immortality. However, when Black☆Star arrives and uses sword strikes against him, Free goes out of his way to try to avoid them, immediately tipping Kid off that the Free in front of them is just an illusion that he created to stall for time, as the only reason why he would have to avoid them is because a solid hit would have passed through him and revealed the illusion, not to mention an immortal would have nothing to fear from such attacks to feel the need to dodge them.
- In Spy X Family, Loid was able to figure out Yuri was a member of the Secret Police because of how he bought the wine, recognizing it as a cover story in the government agency's handbook. However he was certain of it when Yuri stated the price as the same as in the handbook, having not realized the price for that wine went up due to a poor harvest.
- What does in one fake in Tiger Mask: while initially the real deal wears an armband and avoids illegal moves, he eventually loses it and begins fighting like a Heel. By the time the dust settles, the winner is a man with a tiger mask and plastic fangs. The faker had steel fangs.
- In Tsubasa -RESERVoir CHRoNiCLE-'s Drama CD omake, Shiritsu Horitsuba Gakuen, Kurogane figures out Yuui-sensei's real identity by literally spotting a thread on the man's shirt; Kurogane had mended a button on Fai-sensei's shirt with a different-colored thread earlier, and the impostor's shirt button was held together with thread of the original color.
