Continuity mistake: At the beginning of the episode where they are watching Ross through the window, Phoebe is leaning forward and standing to the left of the pole next to Chandler. When the shot changes to Ross coming through the door, she is suddenly standing up straight and is now behind Joey and Chandler.
Continuity mistake: When Rachel and Joey are at Joey's apartment throwing wet paper towels at the entertainment unit, Phoebe comes in to ask Rachel to switch back to Monica's apartment. During the scene, Phoebe is standing in front of the entertainment unit, and the wet paper towels' number and positions change between shots.
Continuity mistake: In previous episodes we've seen that from the living room there's a short wall just inside Monica's bedroom (presumably to prevent a clear view inside, as her bedroom set isn't normally there). However in this episode when most of the gang are in her room, they're listening right by the door into the living room with nothing in the way.
Continuity mistake: After Chandler has been playing the Ms Pacman machine all day he claims his hand has seized up and it appears to look like a claw. From then on in that scene, his hand manages to move around fine. It goes in his pocket, and he waves it around like normal, and then when he mentions his hand again at the end of the scene, it appears to have seized and is clawlike again.
Continuity mistake: Near the end when Rachel runs after Phoebe and Mike to ask Mike if the guy from the bar called, she leaves the apartment with her bag, which she places over her left shoulder. When she is talking to Mike the bag is gone, and then when she returns to the apartment she has her bag again.
Other mistake: When Joey comes out the bathroom in the girls' apartment with a turkey stuck on his head, the bathroom floor has the black and white tiles. But that floor wasn't there until Joey put it there in Series 3, The One With Frank Jr. So in the flashback the bathroom floor should be white tiles.
Continuity mistake: When Ross arrives at the classroom late and out of breath, he tosses his jacket at the hook, but it falls to the floor, and he walks behind the desk anyway. In the next wideshot of the class, as Ross still stands behind the desk, the coat is up on the hook. (Viewed on broadcast TV as a rerun, so there may be a missing shot that was removed for extra commercial time.).