During Nibbler's birthday party, Bender becomes annoyed at how little attention he is getting and flushes Nibbler down the toilet. Distraught, Leela wishes that Bender could understand human emotions, so Professor Farnsworth installs an empathy chip in Bender so that he can feel Leela's emotions as she feels them. Leela's sadness of losing Nibbler becomes too great for Bender, who flushes himself down the toilet to find and rescue Nibbler in the sewers. Fry and Leela follow Bender and encounter a group of sewer mutants who live in fear of a monster called El Chupanibre, believing it to be Nibbler. Nibbler returns safely, but it turns out that he is not the monster, which appears alongside him. Bender tries to fight El Chupanibre, but Leela's fear for Nibbler's safety immobilizes him, so he convinces her to think only about herself rather than others, which gives Bender the strength to drive off the monster. Bender's empathy chip is later removed, though he has learned nothing.