I love this episode!
The main story is that Ross gets an allergic reaction from some Kiwi Pie that Monica made but is looking after Ben. He needs to go to the hospital though, and so entrusts Joey and Chandler to look after Ben while he goes to get treatment.... Joey and Chandler decide to use Ben as a babe magnet and end up getting on a bus with some women, only to then get off the bus and leave Ben on it!!!
When they go to pick Ben up they can't decide which Baby is Ben so decide to flip for it:
Joey: Uh... uh, we'll flip for it. Ducks or clowns?
Chandler: Oh, we're gonna flip for the baby?
Joey: You got a better idea? Chandler: All right, call it in the air.
Chandler: Heads it is.
Joey: Yes! Whew!
Chandler: We have to assign heads to something.
Joey: Right. Okay, okay, uh... ducks is heads, because ducks have heads.
Chandler: What kind of scary-*** clowns came to your birthday? Only when they get home do they realise they have the right baby when he starts to cry around Monica like before!
Overall a great funny episode!