As Mike moves in with Phoebe, he is startled by the presence of rats and advises Phoebe to set up traps. Phoebe, however, states the rat Mike saw is named Bob and that Mike is eating Bob's crackers. Mike manages to convince Phoebe to set up traps, but Phoebe is initially unaware the traps will kill Bob.
As Phoebe realizes Mike's traps will kill Bob, she and Mike attempt to remove all traps. In this process, Phoebe discovers a nest of baby rats in the cupboard, which leads her to realize Bob is female. Moments later, one of the traps kills Bob. Phoebe, feeling increasingly guilty, decides to "adopt" the baby rats and be their mother, going as far as taking them to Monica's party, much to the latters dismay.
Mike tries to convince Phoebe to give up the baby rats, since according to him, they will reproduce and there will soon be hundreds of them. Phoebe believes the rats wouldn't reproduce with their siblings, but then discovers a disturbing sight in the box where she keeps the rats, causing her to scream: "Get off your sister!"
Phoebe later states all baby rats "have gone to good homes."