Continuity mistake: The first time Phoebe and Monica are making bets on when Rachel will give birth, Phoebe has a bottle of water in her hand and is holding it near her stomach. She puts it to her mouth to drink some, but in the next shot, the bottle is near her stomach again.
Continuity mistake: In the one in Barbados, part 2, when Ross and Charlie are hiding behind the plant from the other scientists, the drinks they are holding refill themselves and Charlie's ornament in her drink keeps switching sides of the glass.
Continuity mistake: Ross claims he looks into Monica and Chandler's and watches them eating dinner and watching TV. His apartment is a floor lower down than theirs and with the balcony wall, the sofa and tables distance from the window and the fact the bottom of the window is higher than the floor, there is no way Ross would be able to see that far in. We have seen in the past that he can basically only see who is at the window.
Continuity mistake: When Phoebe is being removed from her "bucket spot" she starts to take off the signs she has put up. With the camera close up to her, she rips one off, then the camera changes to a wide view, and she is suddenly holding two signs.
Continuity mistake: When Chandler, Ross and Monica are in Central Perk discussing playing bagpipes, and Ross says, "Decide whatever you want," he is gesturing with his right hand up and with an open book in his left hand. When the camera angle changes, the book is closed and is now in his right hand.
Continuity mistake: When Monica, the fake Monica and Rachel are in the girls' apartment talking about the two Monicas auditioning for CATS, Monica (real) has a baguette and a bowl of sandwich filler on the table. In one shot of all three of them, she opens the baguette and starts filling it, then the camera goes in for a close-up of the real Monica and she opens the same baguette and starts filling it again.
Continuity mistake: When Monica comes round to Phoebe's, Phoebe reminds her that she's got to clear out stuff. In this wide shot Monica has both hands by her sides, but when it cuts to her finishing saying "oh right", her right hand is now gripping her bag's strap.
Continuity mistake: When Monica and Phoebe are eating with the diplomat and his translator, watch the translator's chocolate cake. It either rotates, has some taken out of it, or is a different piece. Whichever way, the cake changes size, shape or position without him ever touching it.
Continuity mistake: When Monica and Mike play table tennis and Monica says "I think that may have missed the table" there is no one sitting in the chairs behind her. The shot then cuts to Mike and he replies "oh do you?" The shot then cuts back to Monica, she replies "er, yeah" and there are suddenly two people sitting in the chairs behind her. Then in the next shot of Chandler and Phoebe the women who were just in the chairs are now walking behind Chandler and Phoebe in the direction of the chairs, and in the next shot they take their seats.
Continuity mistake: During the scene when Chandler arrives with his test results, Phoebe is reading a book with a red section on the left hand page. In the next shot, the red on the page has vanished. Then, in the next shot, the red page is back again. Also Phoebe's left hand moves between shots.