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.
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.
The One Where Ross Moves In - S5-E7
Continuity mistake: Rachel tells her neighbor Danny that she doesn't know anything about sailing, but later in the series, Rachel teaches Joey how to sail after he wins a boat at a silent auction. She says she learned sailing from her father while growing up.
Continuity mistake: When Ross is talking to Phoebe and Joey in Central Perk, a strand of Phoebe's hair keeps getting snagged behind the buttons of her blouse and hanging loose again with her other hair several times during the scene. (00:12:40)
The One Where Rosita Dies - S7-E13
Continuity mistake: When Chandler and Rachel figure out that the chairs were switched they both head over to Joey's apartment. When they enter the apartment, the new black chair can be seen with tags attached to the top and left side. When the scene cuts to Joey sitting down the tags are all missing from the chair. (00:20:05)
The One After Joey And Rachel Kiss - S10-E1
Continuity mistake: Chandler, Monica and Phoebe are shown listening at the wall between their room and the room Ross is in with Charlie. However, when Ross comes into the room, the outside hallway is shown, and it is clear that the wall they were listening at actually connects to the hallway, not another room. Ross even walks in that direction when he leaves, proving it's not a dead end or similar. (00:05:30)
The One With Princess Consuela - S10-E14
Continuity mistake: When Phoebe and Mike are at Central Perk discussing their name changes, his scarf goes from being hung loose around his neck to tied around his neck from shot to shot. (00:12:15)
The One With The Cake - S10-E4
Continuity mistake: Just before Rachel and Ross come back from the cake store, Monica is holding Emma on her lap. Emma is holding a green toy in one shot, when the camera angle changes it is nowhere to be seen. (00:19:30)
Continuity mistake: In the hospital when Erica is giving birth and the camera is on the doctor, the door to the room is closed. However, when the camera angle changes, the door is wide open even though no one had entered or exited.
The One With The Cake - S10-E4
Continuity mistake: At the end after Rachel and Ross have come back from the cake store, when they are asking Emma how old she is, we can see Joey walking to sit down, then in the next shot he is sat down, then walking to sit down again. (00:20:25)
The One Where The Stripper Cries - S10-E11
Continuity mistake: When Ross and Chandler are talking about who broke which pact in college (the girls they agreed not to date) they are standing at the drinks table. Chandler is holding a drink in his left hand and his right hand is in his pants pocket. The shot then changes to face Ross, Chandler does not remove his hand from his pocket, but in the next shot facing him his drink is in his right hand. He then places it on the table. (00:18:20)
The One With The Cake - S10-E4
Continuity mistake: When Monica's mum and dad are leaving the party, they are standing next to each other while her dad explains why he can not drive anymore. Her mum has both hands in front of her holding on to her purse, in the next shot one arm is around Monica. (00:13:50)
Continuity mistake: When Joey wakes up all covered in sand, his right "breast" has a big crack. But when the camera angle changes, the crack has gone.
Suggested correction: The crack comes and goes as he breathes.
The One With Phoebe's Rats - S9-E12
Continuity mistake: When Monica goes to Rachel's office and invites Gavin to Rachel's birthday party Rachel gets up and goes to the door exclaiming "why did you invite him, I hate that guy." She has nothing in her hand when she gets up from her desk; but at the very end of the scene when she tells Monica to be quiet, she's got a pen in her hand for one shot. (00:12:45)
The One With The Memorial Service - S9-E17
Continuity mistake: After Phoebe kisses Mike in her apartment, Mikes friend rushes in and discovers them. As soon as the shot widens, Mike's hand moves from being behind Phoebes head to his lap. (00:17:35)
The One After Joey And Rachel Kiss - S10-E1
Continuity mistake: When Ross and Charlie are sitting on the bed it shows Charlie fixing her T-shirt. In the very next shot her hands are on her lap. (00:04:25)
The One With Phoebe's Rats - S9-E12
Continuity mistake: At the party, when Monica and Rachel are talking about Gavin, Rachel has a napkin in her hand at one shot, the shot changes and the napkin is replaced by a drink. (00:13:20)