Quote from Phoebe in The One with Phoebe's Rats
Mike: Oh, God! Phoebe: What? Mike: Okay. I don't want to freak you out or anything but I just saw a rat in your cupboard. Phoebe: Oh, yeah. No, that's Bob. Mike: Well, he's your pet rat? Phoebe: Well, not so much a pet as, you know, an occasional visitor who I put food out for. Kind of like Santa. Except Santa doesn't poop on the plate of cookies.