The One With Rachel's Sister - S6-E13
Continuity mistake: When Jill drops her shopping bags on the coffee shop table, the small blue Tiffany's bag is visible on the end of the 'line'. But it is not visible in any shots after Rachel comes in. Additionally, when Rachel grabs the bags and leaves, Ross seems to pick the little blue bag up off the floor, though it is not shown how the bag got there. (00:05:35)
The One with the Thumb - S1-E3
Continuity mistake: When Joey comes into Monica and Rachel's apartment and sits down, he puts his towel on his lap. In the next shot it is over his shoulders, then back on his lap again. (00:18:30)
The One With the Male Nanny - S9-E6
Continuity mistake: The hallway outside Ross' new apartment (series 6 onwards) always changes. Sometimes, the apartment is at the end of a dead-end corridor, and there is a plant outside, covering up the wall; sometimes you can go past the apartment and turn left or right; or, as in this episode, you can only turn right immediately after you have passed the apartment. (00:26:00)
The One Without The Ski Trip - S3-E17
Continuity mistake: Just before Ross leaves the rest stop, Phoebe goes over to him and says,"Maybe we can see a movie or something. Or the rodeo." When she says this, she takes a step back from Ross twice. (00:20:20)
The One With The Princess Leia Fantasy - S3-E1
Continuity mistake: When Joey says "we'll call that plan B, all right?", Monica has her chin in her hand. When it cuts to a different angle, she's got both arms on the table. Rachel also goes from having both hands clasped under her chin to having one arm resting on the table and one reaching for coffee. (00:05:10)
The One With Monica's Thunder - S7-E1
Continuity mistake: When Joey is asking how old he looks, his hands are in his pockets. In the next shot he is gesturing, then instantly his hands are back in his pockets. (00:09:00)
The One With Rachel's Date - S8-E5
Continuity mistake: When Ross asks Rachel how the date went, she grabs the bag she is holding. Next shot she is touching her coat. (00:18:20)
The One with the Blackout - S1-E7
Continuity mistake: At the end of the episode, as Chandler turns to the security camera, he is stood right next to the door. In the next shot he has jumped about 2 feet away from the door instantly. (00:21:20)
The One With Ross's Library Book - S7-E7
Continuity mistake: At the very beginning, Joey is eating some cereal and then says he has to go to work, so puts it down on the table - but in the rest of the scene it vanishes. (00:00:15)
The One Where Chandler Can't Cry - S6-E14
Continuity mistake: In the cafe, Ross says to Rachel, "I'll tell her we can't see each other any more," and we see Rachel bring her hands down from her face. However, in the previous shot we had already seen her lower her hands. (00:03:25)
The One With Joey's Award - S7-E18
Continuity mistake: When Rachel and Joey are talking, the syrup bottle moves from the label facing Rachel to the label facing the camera. (00:05:50)
Continuity mistake: On the plane, when Rachel says "She's almost never right," (about Phoebe) you can see the guy's hand is on the armrest. Then a split second later, his hand is about half a feet off the armrest while saying "But she is sometimes." (00:15:15)
The One Where Monica Gets a Roommate - S1-E1
Continuity mistake: During Monica's date, she points her fingers and asks, "What were you going to say?" In the next shot she is gesturing with her hand. (00:16:00)
The One Where Monica and Richard Are Just Friends - S3-E13
Continuity mistake: When Monica is in Richard's room she lights candles then realises Richard's home with another woman so blows out the candles but misses one. Next she hides under the duvet waiting for Richard. When he comes in all candles are unlit but she is still under the bed. (00:18:00)
The One With The Nap Partners - S7-E6
Continuity mistake: Monica and Chandler are in their apartment talking about Monica's worries that Chandler would dump her if she put on weight. When we first see Monica, the bite mark in her apple is quite small, but a few seconds later, it is suddenly much bigger without her eating any more of it. (00:18:00)
The One with All the Poker - S1-E18
Continuity mistake: When the group is sitting around the table in Monica's apartment playing poker, Monica is making something to eat. When she puts it on the table and sits back, we can see a pile of plates on the table on her right side. But in the next shot, the plates are gone. (00:05:35)
The One On The Last Night - S6-E6
Continuity mistake: At the end when Monica and Chandler hug, Monica's arms keep going from under to over Chandler's arms as the cameras switch many times. (00:20:00)
The One With Rachel's Phone Number - S9-E9
Continuity mistake: In the scene where Joey is sitting in front of his door with the baseball bat, the bar stool is directly in front of his door. When he stands up the chair does not move. However when he and Chandler come back to the hall the chair is over in the corner next to his door. (00:16:00 - 00:19:35)
The One With Ross's Wedding, part 2 - S4-E24
Continuity mistake: As Ross says, "This is our wedding day," in a close-up, Elliott Gould is holding a bit of paper in his left hand (glasses in his other hand, out of shot). In the wide shot, the paper is in his right hand, then jumps back to his left when the angle changes. (00:36:25)
The One That Could Have Been, part 1 - S6-E15
Continuity mistake: Near the start, Chandler is sitting in the coffee house in the big chair. When he's talking to Joey about money, his feet change positions every two seconds. On the floor, crossed, resting on the table, the list goes on and on. (00:04:55)
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.