Continuity mistake: In the scene when Joey and Chandler come into the cafe to say that Marcel got into San Diego zoo, the man who wants him for animal fighting turns and says that Ross is making a big mistake. At this point the monkey starts to go down Ross's arm and almost drops off but in the next shot he is far up on his shoulder again.
Continuity mistake: After Monica says "Oooh can we lie in our vows?" it cuts to Rachel then back to Monica leaning on her hands, but when it goes for a close up she is holding the pen in her right hand, there isn't enough time for her to naturally pick it up.
Continuity mistake: The night before they go to the baby furniture store, Ross and Rachel are in the kitchen talking. Just before they leave the kitchen watch Rachel's robe: in one shot the 'lapels' are neatly one over the other, and in the next shot one lapel has moved lower and looks halfway folded over as if she hastily pulled the robe together.
Continuity mistake: Jill goes to Ross' place, intending to make Rachel mad. When Ross goes to Rachel's to talk to her afterward, she rolls up her sleeves saying, "I'll give you something to think about." When Rachel is next shown, her sleeves are rolled down. Her arms also go from by her sides to crossed in front of her.
Continuity mistake: When Ross say 'just a smidge' after Rachel says Paulo named her breasts, Phoebe is holding tinsel and Rachel is looking at Ross. In the next shot, Rachel is looking in the opposite direction and the tinsel has vanished from Phoebe's hands.
Continuity mistake: In the scene where Joey is sitting in front of his door with the baseball bat, the bar stool is directly in front of his door. When he stands up the chair does not move. However when he and Chandler come back to the hall the chair is over in the corner next to his door.
Continuity mistake: As Ross says "this is our wedding day", in a close-up Elliot Gould is holding a bit of paper in his left hand (glasses in his other hand, out of shot). In the wide shot the paper is in his right hand, then jumps back to his left when the angle changes.
Continuity mistake: During the Monopoly game (deleted scene), right after Monica says, "we can bring my wheelbarrow, to carry your teeth," we see Ross reading the game manual at the end of the shot. At the beginning of the very next shot, he is suddenly rolling the dice with no manual in his hands.
Continuity mistake: When Ross is telling Rachel and Phoebe about Charlie's past boyfriends, he refills two wine glasses. Then in the next shot, he puts his hands to his cheeks in shock because he just remembered something, without putting the wine bottle on the table. It just disappears from his hands.