The Professor failing to consider the brain immune response makes the perfect excuse for body swapping shenanigans.
What happens in Cygnus X-1 stays in Cygnus X-1
As Bender plans to steal the crown of a Robo-Hungarian prince, Fry and Leela question the depth of their relationship, and Amy would very much like to begin unhealthily eating out of control again. But when it turns out the professor's mind switching machine cannot work on the same two people twice in a row, the plot spirals out of control as Planet Express and then some begin using the machine for their own nefarious purposes.
Professor Farnswoth runs away and joins the Robot Circus, Scruffy and Washbucket admit their love for each other, Amy binges in three different bodies, Bender has to give a speech to the UN and Fry and Leela go on a date as Zoidberg and Farnsworth to try and prove that the other only cares about looks. In the end though, everything can be fixed with math. And robot clowns.
Tropes present:
- An Aesop: Be happy with who you are. Laid out by Big Bertha, who may be old and breaking down, but she prefers it to changing who she really is.
- Am I Just a Toy to You?: Leela believes Fry only loves her for her looks and switches bodies with Amy who is in the body of the professor. Fry tries to teach her a lesson by switching bodies with Zoidberg to prove she isn't attracted to him in a gross body. Eventually, they prove their true devotion to each other and have sex in their equally gross bodies.
- And This Is for...: After Big Bertha sacrifices herself to let the professor reach the prince in time to save him, he announces "this is for Big Bertha". However this is subverted as the professor actually misses and corrects himself by saying "That is not what I meant to give you for Big Bertha".
- Balloon Belly: Being able to give into her real appitite for once. Amy is able to make Leela's body gain a large amount of weight in a relatively short amount of time.
- Bluff the Imposter: Bender is asked to prove he actually is a robot. He chooses his break-dancing skills. It works.Basil: He steps forward yet moves backwards!Nikolai: By the gods! He is a machine!
- Body Surf: Everybody does a bit of this, especially when it's time to get back into their normal bodies.
- Call-Back:
- Bender's poor grasp of math comes back to bite him when Emperor Nikolai asks him to prove he's a robot.
- Robo-Hungary, introduced back in The Honking is important to the plot.
- The Harlem Globetrotters get called in for their math skills once more.
- The mind-switching machine is apparently related to the one the Professor used back in Bender's Game. Amy complains about having to clean up the heaps of dead monkeys it caused.
- Amy's childhood obesity is brought up again.
- Chainsaw Good: The swords Basil and the Professor use also function as chainswords.
- Clown Car: The clowns at the Robo-Hungarian circus use Bender's body as one.
- Cool Sword: Nikolai's cousin Basil fights with a sword that functions as a chainsaw.
- Didn't Think This Through: Bender’s heist doesn’t go according to plan since he can’t swap bodies with everyone quickly.
- Excuse Plot: There's no central plot other than disorganized chaos around the rapidly switching bodies.
- Epic Fail: The Professor in Bender's body draws a sword, and tries to stab Basil... and misses completely.
- Fan Disservice: Leela and Fry sitting to a romantic dinner at Elzar's restaurant jump up onto their table and begin making out... in Zoidberg and Farnsworth's bodies. On the bright side, it cures Amy of her desire to eat (ever again) and loses Hermes' body some weight.
- Also Zoidberg showing Fry and Hermes the barnacles on his tuchus.
- Fanservice: Bender in Amy's body dresses in a bikini. Washbucket in Amy's body dressed in a negligee when she tries to seduce Scruffy.
- Faux Horrific: The Professor's declaration that they need to use math is met with a lean-in and dramatic music.
- Femme Fatale:
- As mentioned above, Bender uses Amy's body in an attempt to distract Emperor Nikolai's guard. It fails, on account of the guard being a robot, and Bender being... well, Bender.
- Princess Flavia.
- "Freaky Friday" Flip: Notable in that, while most ""Freaky Friday" Flip" plots use magic or don't explain why two or more people switch personalities (other than it being An Aesop about learning perspective and "walking a mile in someone else's shoes"), the reason why two or more people are switching personalities is part of a criminal plot gone wrong rather than a "two different people argue over who has it tougher" plot.
- Grand Theft Me: While nobody is forced to switch bodies, they are rarely honest in how they go about it. Then Farnsworth runs off with Bender's body to join the circus.
- Heist Episode: Bender plans to steal the royal jewels of the Robo-Hungarian Empire, and tries to recruit the others as his Caper Crew. When they refuse, he has to go at it alone, with less than stellar results.
- Here We Go Again!: After Bender realizes he accidentally left Robo-Hungarian Emperor Nikolai's jewels inside the latter's body, he immediately resolves to form a Caper Crew to steal them, just as he tried to do at the start of the episode.
- Heroic Sacrifice:
- Big Bertha fires Farnsworth in Bender's body so that it can reach the United Nations to save Bender in Nikolai's body, even though the blast will end up destroying her already battered body.
- In a lesser vein, Hermes lets Amy use his body so she won't ruin Leela's body further. She won't have to worry about ruining Hermes' body because "thirty years of the munchies beat you to it."
- Ignore the Fanservice: The reason Bender stole Amy's body was to utilize her body to seduce the guards. This fails the minute he encounters Basil, who as a robot obviously isn't going to be distracted by a human woman. Bender has to resort to punching him out.Amy!Bender: (after punching him out) I said, "Bakka wow, bakka wow wow..."
- Insane Troll Logic: Leela, suffering from body image problems, is running on it. She asks Fry how he feels about her eye, and when he tries to be supportive, criticizes him for it, something that makes Fry do a double-take.
- Lost My Appetite: Amy is finally cured of her obsessive eating after seeing Fry and Leela making out in Zoidberg and Prof. Farnsworth's bodies.
- Manly Tears: Scruffy sobs on the couch after having to have a Stiff Upper Lip rejecting Mop Bucket's Anguished Declaration of Love.
- Mundane Luxury: Zoidberg in Fry's body marvels at Bender and Fry's humble apartment, several steps up from Zoidberg's home in the garbage bin. "A floor? We live like kings!"
- Mundane Made Awesome: When asked if there's a way to get around the limitations of the mind-switching machine, Professor Farnsworth (in Bender's body) dramatically declares "I'm afraid we need to use... math!", which is followed by a dramatic sting.
- Nutritional Nightmare: One of the foods that Amy eats in Leela's body is a deep-fried ice cream sandwich wrapped in frosting and lightly baconed, which she proceeds to eat with ketchup.
- Sexy Discretion Shot: Fry and Leela apparently have sex off screen in Zoidberg and the professor's body... for which the audience is profoundly grateful.
- "Shaggy Dog" Story: Bender attempts to steal Robo-Hungarian Emperor Nikolai's jewels while in possession of his body, and once everything is resolved...Nikolai: So long, filthy commoners!
Bender: ¡Adios! And I'm left with the real jewels safely inside... (Looks inside his chest cabinet.) HIS COMPARTMENT?! AW! All right, I'll need accomplices. - Shout-Out:
- The title and Bender’s plot are a homage to The Prisoner of Zenda
- In order to test Bender in Amy's body, Basil and Nikolai employ a reverse Turing Test, an inversion of the Turing Test, which is when a computer can pretend to be sufficiently human.
- The sign on the U.N. building is a dead ringer for the sign welcoming visitors to Las Vegas.
- Shown Their Work: As mentioned before, this episode is notable for having episode writer Ken Keeler create the Futurama theorem, a real-life mathematical theorem invented purely for use in this episode, proving that regardless of how many mind switches have been made, they can still all be restored to their original bodies using only two extra people, provided these two people have not had any mind switches prior.
- Star-Crossed Lovers: Scruffy and Washbucket genuinely love each other, but their love can't go anywhere on the basis that Scruffy is human and Washbucket is janitorial equipment. When Washbucket tries to circumvent this with Amy's body, Scruffy almost runs away with it but can't bring himself to do so, seeing the union as "wrong" and being unwilling to ruin Amy's life.
- Temporary Bulk Change:
- Amy manages to get Leela's thin and attractive body fat, which she uses to angst to Hermes, who is also feels troubled with his body. Leela's body manages to get better at the end of the episode though.
- Hermes, who is normally tubby, actually becomes thinner at the end of the episode while Amy was in his body, which was caused by her suddenly losing her appetite after witnessing Leela and Fry making out in Farnsworth's and Zoidberg's bodies respectively. He is back to his normal self the next time he appears.
- Thrill Seeker: At first Farnsworth thinks he can use Amy's young, healthy body to finally have an exciting time, but she's just not invincible enough for the things he wants to do. So he trades Amy's body to Bender, and uses Bender's body to run off and join the Robot Circus as Nonchalanto, the world's most indifferent robot daredevil. He even comments to Big Bertha that he's always longed to be shot out of something, and politely asks if she'd fire him out of her cannon.
- Unexplained Recovery: Zoidberg in Fry's body and Nikolai in Wash Bucket's body ignite gas and blow it up in Fry's apartment, but in the next few scenes, they are shown uninjured and unaffected.
- Unrequited Love Lasts Forever: Scruffy and his wash bucket will never be able to express their love.
- Unusually Uninteresting Sight: Nikolai's girlfriend takes an impressive lack of interest in learning Bender is a robot in a Chinese-Martian physicist's body.Flavia: How tedious.
- Upper-Class Twit: Nikolai is more concerned with partying, and more partying, than being a responsible leader. He doesn't grow out of it, either.
- Voices Are Mental: Everyone speaks with their own voices, rather than the ones matching their current bodies.
- Weight Woe: After years of suppressing her hunger, Amy takes the opportunity to gorge to her heart's content while in Leela's body. However she's soon depressed at how fat she's made the body, how she can't seem to stop herself from eating and how desperate for food she is (Hermes catches her eating a stick of butter and licking the wrapper).
- Hermes has his own weight woes. When he offers to switch bodies with Amy, she says she'll only ruin his body, too. Hermes sadly replies that it's already ruined.
