Joey: Do you know something?
Rachel: Do you know something?
Joey: I might know something.
Rachel: I might know something too.
Joey: What's the thing you know?
Rachel: Oh no, I can't tell you until you tell me what you know.
Joey: I can't tell you what I know.
Rachel: Well then I can't tell you what I know.
Joey: Okay, fine. [Pause.] You don't know!
Rachel: All right, how about I go over there and I will walk into Chandler's bedroom and I will see that thing that I think that I know is actually the thing that I think that I know!
Joey: [gasps.] YOU KNOW!
Matthew Perry's wit is so legendary that the scriptwriters have often incorporated his gags into the show.