Friends Season 4 Episode 12 : The One With The Embryos
Phoebe's uterus is examined for implantation of the embryos. A seemingly harmless game between the guys and the girls escalates into a full-blown contest to see which pair knows more personal data about the other. The guys end up betting the chick and the duck, and the girls end up betting their apartment. When the guys win, Rachel tells them that it was just a game but the guys continue to move in. At the end, Phoebe tells everyone she's pregnant.