4x11 "The One with Phoebe's Uterus"

Phoebe doesn't know what to do when Frank Jr. visits with his new wife and asks her to carry their child. She visits her birth mother who tells her it isn't a good idea. To support this, she gives Phoebe a puppy, but only for three days to prove it will be hard to give it up. Phoebe decides she will carry their baby because when it's over, they will be so happy, making Phoebe feel good. Meanwhile, Monica teaches Chandler the secrets of a woman's seven erogenous zones, for which Kathy is extremely grateful.