Trivia: Matthew Perry and Bruce Willis starred together in the movie The Whole Nine Yards. While making the movie, Matthew made a bet with Bruce that the movie would open in the top position at the box office. If it did this (which it consequently did) Bruce had to star in an episode of Friends for no fee.
Trivia: In series 10 there's an episode where Phoebe's getting rid of stuff in preparation for Mike moving in, and she dumps two horrendous 3D paintings on Monica and Rachel. I figured they were just created for that show, but in this episode, 4 series earlier, before Rachel goes out for her run we can actually see one of them in the background - nice to see a long term plot device being used. There's even a shot of one of the 3D pictures in the apartment Phoebe shares with her grandmother in season one, when she's calling information looking for her father. One of these paintings can also be been in season 5, the one with all the Thanksgivings, just after Joey scares Chandler wearing the turkey.