Quote from Phoebe in The One with Rachel's Going Away Party
Rachel: Oh, Pheebs, I don't even know where to start. Phoebe: Okay, well, before you do, I know we weren't supposed to get you "going away" presents, but I do have something for you. Rachel: Oh, oh. What is it? Phoebe: Well, it's cotton swab with a bit of my saliva on it. So that if they perfect the cloning process while you're over there, you can use the DNA to create your own Pheebs. Rachel: I'm gonna throw this away, but thank you so much for the gesture.