I Second That Emotion
Nibbler awakens excitedly when he hears Leela opening a can of Kibbles ‘N’Snouts with a gigantic electric can opener. Moments later, Bender enters and accidentally walks under the device, and the blade cuts into his head. Bender recovers from the accident, but voices his disdain for the tiny Nibbler. Shortly thereafter, Nibbler bites Bender’s posterior, chipping one of his fangs in the process. Leela takes her pet to a veterinarian, who pulls the tooth and replaces it with another fang.
Fry notices rings in the tooth, which, like a tree, Indicate Nibbler’s age. Soon after, Leela throws Nibbler a fifth birthday party. Bender grows increasingly jealous of the attention lavished upon Nibbler. Nonetheless, he bakes Nibbler a cake so delicious that he believes it will make everyone worship him. But when Bender leaves the huge, elaborate cake unattended for a moment, Nibbler swallows it down in one gulp. Angered, Bender flushed Nibbler down a toilet. When Leela discovers what happened, she tells Bender he has no regard for anyone else’s feelings.
As the staff gathers to memorialize Nibbler, Bender cold-heartedly turns his attention to All My Circuits. Leela wishes that Bender could feel the same emotions she is experiencing. The Professor then announces that, through the miracle of science, he can make her wish come true. A short time later, the crew pins Bender down, and the Professor replaces one of the robot’s computer chips with a device that will force him to feel Leela’s emotions. When Bender comes back online, he does, Indeed, experience the same emotions as the grieving Leela.
Eventually, Bender is unable to endure her enormous pain. He decides to take a more proactive approach to the situation …and flushes himself down the toilet, piece by piece, hoping to find the missing Nibbler. When Leela and Fry discover what happened, they decide to venture into the sewer system so they can locate their friend. Amy warns the pair that mutants inhabit the underground. But Leela dismisses the idea, labeling it "urban myth."
Later, Fry and Leela venture into the sewer system, and eventually happen upon some contorted-looking beings with pale complexions and pink eyes. The pair realize that mutants living in the sewer system are not urban myth after all. Three of the mutants, Raoul, Dwayne and Vyolet, insist they are harmless. To prove this, the mutants escort Fry and Leela to their village, which is comprised of small buildings standing in liquid.
Leela explains that she and Fry are searching for her pet, Nibbler, which was flushed down a toilet by mistake. The mutants escort the pair to the downtown district, which is filled with goldfish, parakeets, crocodiles, pornographic magazines and anything else flushed into sewer systems from above. The mutants then broach the subject of El Chupanibre, a legendary, terrifying creature that lurks in the darkness. Leela comes to believe that El Chupanibre is, In actuality, Nibbler. The mutants hope to attract and ultimately capture the creature by tying "virgin" Leela to a post in the middle of town
The mutants, Fry and Bender then hide themselves and await Nibbler’s arrival. Eventually, Nibbler emerges from the shadows. But shortly thereafter, a gruesome monster with giant teeth and bear-like-claws the once-thought-mythological El Chupanibre—also appears. In an attempt to save Leela from certain death, Fry runs out toward the center of town square. Unfortunately, he inadvertently steps in a rope-trap meant for El Chupanibre. He is yanked skyward and bounces upside-down in the air.
El Chupanibre, meanwhile, advances upon Nibbler. Leela asks Bender for his help, but the robot is so overcome by Leela’s fear (courtesy of the chip implant) that he is unable to function. Believing it is their only hope for survival, Fry instructs Leela to stop caring about Nibbler. Leela begins thinking greedy thoughts…allowing Bender to function once more. The robot kicks Nibbler out of harm’s way, then knocks the creature into a giant toilet-like fountain, flushing El Chupanibre away.
Later, the Professor reenters Bender’s system and removes the implant chip.