Other mistake: When Rachel attempts to board the plane the first time, the man at the desk looks at her passport upside down.
The One With Ross's Library Book - S7-E7
Visible crew/equipment: When Ross says, "I work here," there is a stage light at the top to the right of Ross's head. (dvd)
The One With Ross's Library Book - S7-E7
Continuity mistake: When Chandler says "lie" his hand is by his side, then up. (00:07:20)
The One Where The Stripper Cries - S10-E11
Visible crew/equipment: In the scene with the conversation with the stripper, there is a large vase on the kitchen table. Several lights, the top of the stage and a few crew members are reflected in it.
The One Where Paul's The Man - S6-E22
Continuity mistake: In the opening scene in Central Perk when Paul (Elizabeth's dad) takes Ross to one side to talk to him you can see the girl in the blue top enters the door twice: first the shot after Paul says "I'm funny like that" and then again after Ross says "I realise it upsets you".
The One Where Chandler Doesn't Like Dogs - S7-E8
Continuity mistake: When Chandler is looking over Ross' list (right before he calls him Magellan), he has the front sheet of the paper folded up. In the next shot, the sheet is folded down.
The One With All The Candy - S7-E9
Continuity mistake: In the scene where Monica's female neighbour comes begging for candy, after Monica gives it to her and shuts the door it's a man standing at the door not the neighbour.
The One With Joey's Bag - S5-E13
Visible crew/equipment: When Joey walks into Monica and Rachel's apartment to tell the gang he didn't get the part thanks to the bag, as he approaches the couch you can see the end of the stage over Joey's right shoulder. (00:21:15)
The One In Barbados, part 2 - S9-E24
Visible crew/equipment: Right before Ross' speech begins, as the camera pans down, if you look at the top of the screen, you would be able to see the top of the set and a set light. (00:31:20)
The One Where Rachel Has a Baby, part 2 - S8-E24
Continuity mistake: When a nurse is putting Emma to bed we see that Emma is nicely wrapped up in a blanket. The shot then cuts and Emma's right arm is sticking out the top of the blanket.
The One With Frank Jr. - S3-E5
Continuity mistake: When Frank has the towel wrapped around him, the knot on his chest changes a lot between shots.
The One With Frank Jr. - S3-E5
Continuity mistake: In the scene where Joey and Monica discuss changing her bathroom tile, Joey moves the hamper to the middle of the doorway and when he kneels down to measure, the hamper is back against the wall. (00:06:25)
The One With Phoebe's Cookies - S7-E3
Visible crew/equipment: When Ross asks what do with all the cookies, a boom mic can be seen at the top of the frame. (Full-screen version only).
The One In Vegas, Part 2 - S5-E24
Continuity mistake: When Monica puts the blue jumper up her dress, she lifts it up and you can see she is wearing black jeans underneath. The next scene shows her running off without the jeans underneath her dress. (00:18:55)
The One with the Thumb - S1-E3
Continuity mistake: When Rachel says, 'One can never be too Alan, ' we see the stick pom-poms that Ross is holding are up facing Monica, but in the next shot the pom-poms are facing the floor, but after Chandler says 'I personally could have a gallon of Alan' in Monica's closeup we see the stick pom-poms are up again facing Monica. (00:11:30)
The One Where Eddie Moves In - S2-E17
Continuity mistake: In the previous episode, Joey tells Chandler that the bathroom in his new apartment has mirrors on both sides of the toilet. But in this episode, when we see the toilet from the side while Joey gives the gang a tour, it is clear that the wall is devoid of mirrors.
The One with Mrs. Bing - S1-E11
Continuity mistake: While everyone's at the restaurant Rachel dips a tortilla chip into guacamole and gets some on her hand. When Paolo takes a bite from the chip he also eats the guacamole off Rachel's hand while she's still holding the rest of the tortilla chip, but in the next closeup Rachel's hand is empty, then in the next shot the remaining tortilla chip reappears in Rachel's hand. (00:06:45)
The One With Rachel's Assistant - S7-E4
Continuity mistake: Ross has always said that Carol was his first (and only, until Julie) sexual partner, but in the episode where they tell each others secrets Chandler says Ross slept with the cleaner when they were at college. Some people say that Ross had kept it a secret, and that's why it had never come out before, but considering that he categorically states several times over series one and two how he'd only EVER been with Carol, getting quite upset at times, that explanation just doesn't ring true.
The One With Ross's Inappropriate Song - S9-E7
Other mistake: When Chandler finds out that the video marked 'Monica' is just a football game he says, 'This may be the first time I have enjoyed football.' Although in 'TOW The Football' (season 3) he is quite happily watching the Thanksgiving Day game with Ross and Joey.
Continuity mistake: Apparently Ross is Monica's older brother but in "The one where they're going to party", Joey states that the three men are all the same age ("we're 29, we're not women"), and in The One with the Birth Monica says she is 26 and Joey says he is 25. If Joey is younger than Monica, and Ross and Joey are the same age, then there's definitely a mistake somewhere.