Bender becomes envious of all the attention that Nibbler has been receiving. The annoyance culminates when Nibbler devours Bender's homemade cake before he can gloriously unveil it. To get rid of the pest once and for all, Bender carelessly flushes Nibbler down the toilet. Leela is heartbroken and rightfully accuses Bender of lacking remorse. However, the Professor has a way to make Bender experience human emotion. He installs an empathy chip and sets it to Leela's emotional frequency so that Bender can understand her loss. Motivated by misery, Bender heads to the sewers to bring back the missing pet and to put an end to his new-found regret, unaware of the dangerous mutants that inhabit the underground.