Quote from Phoebe in The One with Phoebe's Rats
Phoebe: Listen, I think I left something here. Chandler: Well, somebody left this. Is this yours? Phoebe: No, but I like it. No, I think I left one of my rat babies. Chandler: Well, no. I haven't seen it, but if I do, I'll let you know. Monica: Rat baby! Rat baby! Rat baby! Rat baby! Phoebe: Oh. Maybe that's him.