Factual error: The main part of the episode is played out in Chandler & Monica's hotel room (which is situated in between Rachel's and Ross's rooms). The window is opposite the audience and the door on the right. However whenever we see inside Ross's hotel room, he has a window opposite the audience as well. This is impossible as this should be where the hallway is to get to the main door to Chandler & Monica's room. Also, throughout the episode Monica, Chandler & Phoebe all listen through the walls (on either side of their room) to what the other friends are saying, meaning there must be no gap between Ross's and Chandler & Monica's rooms- making the window in his room geographically impossible.
Continuity mistake: In the scene with Robin Williams and Billy Crystal, there is a shot of Rachel, and her hair is hanging straight down. The next shot of Rachel is from a different angle and there is a section of hair behind her ear; in the shot after that it is hanging straight again, and is then behind her ears again.
Factual error: When Monica rolls an 8 to buy everyone a steak dinner, the one die is positioned with a 5 and 4 facing the camera (the 5 on the left, and 4 on the right). With the die that way round a 1 is always on top. There is no other way to get the 5 and 4 combo. This means that Monica had a 7 on the other die, That is impossible. And so she did not roll an 8.
Continuity mistake: There is a scene in Central Perk where Rachel confronts Chandler about all the kissing he's been doing. She raises her hands up in front of her and tells Chandler to hold on to stop him from getting up from the couch. As he goes to sit back down on the couch she lowers her hands to her lap. The shot cuts to an angle behind Rachel's chair and she is lowering her hands again.
Continuity mistake: When Ross and Rachel are arguing about Rachel telling Phoebe about his fantasy, Ross takes a popsicle out of the freezer and bites it. In the next shot, the popsicle is whole again, with no bites, and Ross takes another 'first' bite out of it.
Continuity mistake: Just after Marcel switches the TV to "SAP," Joey comes back and tells Chandler about Ursula and how she gave him extra food. Chandler is holding a bottle of water, and before the camera cuts to Joey it is open, but when he is talking it is capped, and finally when Chandler says "Score," the bottle is open again.
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 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.).