The One With The Halloween Party - S8-E6
Audio problem: When Rachel greets Mona at the door of the apartment, visually she says "Hi" but the audio is " Hi Mona. "
The One With Chandler's Dad - S7-E22
Character mistake: When Chandler says "and there's daddy", an extra behind him chuckles in time with the studio audience. He's the only one laughing and it happens right on cue with the audience.
The One Where the Monkey Gets Away - S1-E19
Continuity mistake: When Rachel tells Ross that she "kind of lost" Marcel it cuts to an exterior shot from the balcony, and if we look past Rachel and Ross we see there's a table against the wall, under the Maïna La Voyante poster, but that table does not exist in previous or following shots. (00:10:15)
The One With Joey's Bag - S5-E13
Continuity mistake: When Phoebe realises she just met her dad she turns to her friends to share the news, and in the closeup she's holding a pair of 3D glasses in her right hand and Monica's holding a pair in her left hand, but in the next wideshot both of those glasses have vanished. (00:09:15)
The One With Joey's Bag - S5-E13
Continuity mistake: When Chandler speeds up the timer for his turn he places the timer down at the right side of the pillow, but it's at the opposite side of the pillow when he lies down. Then before Monica starts giving Chandler his massage, she sets the timer and places it near the foot of the bed which we see in Chandler's closeup, but in the next shot when she says, "Say goodbye to sore muscles," oblivious to Chandler's pain, the timer is lying by the pillows behind her, near the head of the bed. Note, in the "uncut scene" version, Chandler grabs the timer to speed up his torture, and Monica takes it out of his hand thinking he was going to add more time, then she places the timer behind her. (00:00:25)
The One With The Apothecary Table - S6-E11
Audio problem: When Phoebe puts her feet up on Ross' apothecary table, Ross asks her not to put her feet up on his "new...old sheet." During the pause right after he says "new," there's a cut to a different angle and you can see his mouth form the words "old sheet." Then it cuts to a different angle and we actually see and hear Ross say "old sheet." (00:12:05)
The One With The Lottery - S9-E18
Continuity mistake: After he gets the job Chandler sits on the couch pretending to read a magazine and Joey drops a piece of paper that materialises in his right hand in between shots. (00:19:40)
The One With The Fake Party - S4-E16
Continuity mistake: While Joey spins the bottle and it keeps pointing to Emily, in the shots facing Ross the door behind him goes back and forth from being either closed or wide open, depending on the angle of the shot.
The One With The Fake Party - S4-E16
Continuity mistake: After Rachel spins the bottle and it points to Joshua, when she crawls toward him on her hands and knees the bottle is in front of her knees in the shots facing her, but in the shot facing Joshua the bottle is at her side, near her foot.
The One with All the Poker - S1-E18
Other mistake: During the third game of poker, the bottle of raspberry Snapple on the table has part of its brand name whited out on the label.
The One Where Joey Loses His Insurance - S6-E4
Visible crew/equipment: After Rachel speaks with an Indian accent and comments on Bombay, it cuts to an exterior shot of Central Perk and inside we can see the top of the set, as well as a lighting rig at the ceiling.
The One With the Male Nanny - S9-E6
Continuity mistake: When Phoebe is trying to explain to David that she really cares about Mike the door behind David is closed, but when Mike walks in that door is wide open, and it remains open until it's suddenly closed when Mike warns David that if he ever goes to Minsk he'd better watch out.
The One with the Fake Monica - S1-E21
Visible crew/equipment: After Marcel has humped the chair, when it cuts to Joey walking in saying that there already is a Joseph Stalin, we can see the reflection of a crewmember (presumably female) in the small mirror on the wall who's wearing a black top - and it's not Rachel, the angle is off.
The One With Ross' New Girlfriend - S2-E1
Revealing mistake: At the end, when Rachel and Ross are talking on Monica and Rachel's balcony, the edge of the "brick" wall behind them has a gap in it. The facade is obviously a thin plastic sheet that is made to look like bricks and mortar, and it has pulled away somewhat from the surface it is attached to.
The One With The Tea Leaves - S8-E17
Continuity mistake: When Joey is picking up his bagel off the ground in Chandler's apartment he says something about the bagel hole being to small and he has it in his left hand. In the next shot it shows Chandler making a face and Joey's hand is empty. In the next shot Joey is sitting down and the bagel is back in his hand.
The One With Five Steaks and an Eggplant - S2-E5
Continuity mistake: When Chandler is seducing Jade in Central Perk, he turns to face Ross after handing her the tissues. The camera then cuts to another angle where he is still facing Jade, and then he turns again to face Ross. (00:06:40)
The One With The Embryos - S4-E12
Character mistake: Both lightning rounds at the end of the quiz are significantly longer than the 30 seconds that Ross claims they are. (Even though he is supposedly using a stopwatch to time them.) The guys' lightning round is actually 43 seconds long, and the girls' lightning round is 45 seconds long. (00:14:20)
The One Where Old Yeller Dies - S2-E20
Continuity mistake: When Monica asks Chandler and Joey to take Richard to the Knicks, Joey tells Monica, "We will bring him, but only if he takes the Jaguar." Chandler then drops his head in mortification, and the scene then cuts to focus on Monica's expression. In the right corner of this cut, you can see Chandler is looking ahead, and his mouth is moving saying "what am I supposed to say", but there is nothing being said during this scene. The camera then cuts to a different angle where Chandler lifts his head from the earlier drop just before he speaks to Joey. (00:04:30)
The One After the Superbowl, part 1 - S2-E12
Audio problem: When Phoebe is showing the children her guitar in the library, her voice comes on saying, "I know," when the children are amazed by her guitar. Look carefully - her lips are not moving when she says this.
The One With the Baby on the Bus - S2-E6
Audio problem: When the lady on the street (played by Lea Thompson) is talking to Joey and Chandler, her mouth and her voice are not in sync.
Answer: Usually by the seventh night of Hanukkah you don't know what to get the other person, and you will probably resort to getting the other person something insignificant. Chandler is basically saying that the pen is a stupid gift.