Continuity mistake: When Joey goes to Monica and Chandler's apartment, he goes to the fridge to get something to drink to keep his bladder full for the audition. When he closes the fridge he has two bottles in his left hand. The camera cuts to Monica, then cuts back to Joey. He then has two cans in his left hand and is holding them differently.
Revealing mistake: While Monica and Rachel are talking about Chandler's "jollies to Jaws" Rachel's wearing a colorful flowery top, and after Joey walks in just as Monica takes her seat at the table in the closeup, it's Jennifer Aniston's stand-in, wearing a blue top, who is seated beside Monica. (Viewed in widescreen).
Revealing mistake: When Rachel tells Joey that his agent called and he got the audition for the Broadway play, Rachel's wearing a colorful paisley top, and after Monica says, "Maybe the monkey will be at the audition," in the next shot it's Jennifer Aniston's stand-in, wearing a red plaid blouse, who is standing beside Joey. (Widescreen).
Revealing mistake: When Phoebe and Mike walk into Central Perk and announce they're moving in together, Chandler, Monica, and Ross, who's wearing a sweatshirt and khakis, are all sitting on the couch, and after Phoebe's comment about loading up the Volvo and wanting to be a soccer mom, it's David Schwimmer's stand-in, wearing a blue button-down shirt and jeans, who is seated beside Chandler.
Continuity mistake: In the coffee house, when Ross and Joey are having a fight about Joey's proposal to Rachel, Ross does the "quote gesture" with his hands and Joey says he doesn't know what this means. In TOW the Secret Closet, Joey used it himself when talking to Chandler, in the scene where he asks him to bring a bobby pin to pick the closet's lock.
Continuity mistake: When Rachel takes her gift certificate to the massage parlour to claim her free massage, she hands it to the receptionist and we can see that it has been torn up into eight pieces and taped back together. Yet when Phoebe tears up the gift certificate in a previous scene, we see her tear it into only four pieces before handing it back to Rachel.
Continuity mistake: In TOW the lottery tickets series 9 just after Chandler has got the job and he sits down you can see Joey's hand in the right side of the screen however when the shot changes Joey moves his hands up to the position we have just seen. The shot changes back and his hand is in the same position.
Continuity mistake: In the one with Phoebe's rat babies, it is very obvious that the box has nothing in it. Also when she is in her apartment explaining about giving up the triplets she had for her brother she puts the box down on the table, yet when it cuts to Mike's face and Phoebe's realisation that she hadn't told him that before, the box is back on her lap.
Continuity mistake: When Phoebe says that they should not tell Ross that the date is cancelled so that he gets stood up, Joey says, "I hear that's bad" - implying that he has never been stood up so doesn't know how it feels. However, in TOW Two Parts (Part II), Ursula stands Joey up, and he takes it pretty bad.
Continuity mistake: Towards the end, during a scene at Ross and Rachel's, Sandy picks up two puppets and puts them on each hand. He starts pulling the blue one onto his left hand, but when the angle changes there's a yellow one on his left hand, and a blue one on his right. It cuts to Ross, then when we go back to Sandy they've changed hands again.
Continuity mistake: When Rachel wakes up Emma during a nap, against Phoebe's advice, there is a shot of Emma in the cot. She is wearing a plain pink hat, but in the next shot, when Rachel lifts her out of the cot, she is wearing a white hat with what looks like little flowers on it.
Character mistake: When Monica and Mike are playing table tennis, Monica puts her hand on the table and looses the point. Mike then does the same thing. Surely Monica, of all people would notice that as it would have given her the point. We also see her looking at Mike at the time.