S02E05: I Second That Emotion

Professor Farnsworth installs an empathy chip in Bender, forcing him to feel human emotion. After Bender flushes Nibbler -- Leela's beloved pet -- down the toilet, while showing no sign of remorse, the insensitive robot is programmed to receive Leela's emotional frequency. Overcome by sadness, Bender sets out on a mission to find Nibbler and save him from the dangerous depths of the sewers, where mysterious inhabitants lurk.