The One With Phoebe's Birthday Dinner - S9-E5
Continuity mistake: Phoebe implies that her birthday is round about Halloween - October 31st. However, in The One With Frank Jr in series three, she tells Frank that her birthday is February 16th. (00:00:05)
The One With Phoebe's Birthday Dinner - S9-E5
Factual error: The restaurant refuses to take anyone's orders until they're all seated, which means that the group is sitting, occupying a table, without earning any revenue for the restaurant. There isn't a restaurant in NYC that would have such a policy, since it basically guarantees that a table becomes a revenue vacuum. (It also makes for very unhappy customers, but that doesn't qualify it as a factual error, since some restaurants might be actually stupid enough to not care about their return customers).
The One With Phoebe's Birthday Dinner - S9-E5
Deliberate mistake: Across the whole show, whenever Ross closes his apartment, the door remains unlocked; but in this episode, when he and Rachel go outside, the door locks itself. (00:07:00)
The One With Phoebe's Birthday Dinner - S9-E5
Continuity mistake: Rachel is telling Ross why she doesn't want to go to the dinner, and she says "the first sign is I don't want to, and...I'm not going'. While she says this, her left hand is completely empty, but then in the next shot the camera goes back to Ross and she is now holding the baby monitor in that hand. It then moves around in different shots afterwards. (00:06:10)
Suggested correction: She comes in with that baby monitor and it never leaves the sight of camera.
The One With Phoebe's Birthday Dinner - S9-E5
Continuity mistake: When Pheobe says "One really does have a stick up one's ass," the waiter's hands move from in front of him to behind his back. (00:08:05)
The One With Phoebe's Birthday Dinner - S9-E5
Continuity mistake: Near the start, when Chandler asks if anyone else smokes, a woman with a brown jacket is seen getting a pack of cigarettes out her pocket. The camera cuts and now she has one in her mouth and is lighting it. (00:02:35)