1x21 "The One with the Fake Monica"

When Monica's credit card is stolen, she, along with Phoebe and Rachel, decide to catch the thief, but Monica begins a friendship with her. Joey enlists his friends to help him come up with a less ethnic-sounding stage name. And when Ross finds out that Marcel has reached sexual maturity and needs to be with other monkeys, he tries to get him accepted into the "Harvard of zoos", with an emotional goodbye.