The One With The Video Tape - S8-E4
Continuity mistake: When Ross turns on the camera and sits down in front of it, "flirting" with it and drinking wine, what you can see on the little camera screen is very different from when they play the same clip on the TV, in which looks like he was sitting much closer to the camera then he actually was.
The One With All The Wedding Dresses - S4-E20
Continuity mistake: Rachel takes a drink from the Jones Soda and sets the bottle down. A second later, the bottle is fuller than it was to begin with. (00:10:05)
The One With The Jellyfish - S4-E1
Continuity mistake: When Chandler, Joey and Monica tell their story of the jellyfish bite Chandler says sometimes at night he still hears Joey's voice screaming "Do it ! Do it!". Joey says he yells it through the wall at night to freak Chandler out, but no nights have passed. They tell the story the same day the jellyfish bite occurred. Notice Rachel, Ross and Phoebe are wearing the same clothes they had before they left the beach house. (00:16:20)
The One with the Dozen Lasagnas - S1-E12
Continuity mistake: When Ross says he could escape from any uterus, Joey is holding two small books. In the next shot they have vanished and he is holding a large book. (00:02:10)
The One With The Bullies - S2-E21
Continuity mistake: When Phoebe calls by the house with the dog, a woman with a handbag is visible in the background, going into her house. About ten seconds later we see the same woman with the handbag walk towards her house again. (00:15:40)
The One Where Underdog Gets Away - S1-E9
Continuity mistake: Chandler is able to get into Monica's apartment to tell everyone that Underdog got away, but later when Rachel closes the door it is now locked. We can see the door as each person is leaving and nobody does anything which could be construed as locking the door before it closes. It's been often demonstrated in the show that the door doesn't lock automatically. (00:13:20)
The One with George Stephanopoulos - S1-E4
Continuity mistake: Just before Ross gets hit in the hockey game, you can see him wearing a foam finger which then disappears. (00:11:45)
The One With the Male Nanny - S9-E6
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. (00:24:30)
The One With Joey's Award - S7-E18
Continuity mistake: When taking Jessica's award, Rachel opens the door. But when the camera cuts, Joey is first through the door. (00:18:40)
The One Where Chandler Crosses The Line - S4-E7
Continuity mistake: When Phoebe tells Ross that she wants to hear his "sound", she has her guitar in her lap. The shot changes, she says "Play that funky music white boy," and her guitar is missing. In the next shot, Ross runs out and her guitar is back on her lap again. (00:03:50)
The One With Ross' Step Forward - S8-E11
Continuity mistake: When Phoebe is getting drinks out of the refrigerator, she gets out two different type bottles, and they switch hands during the scene. (00:17:50)
The One In Barbados, part 2 - S9-E24
Continuity mistake: In the final episode of series 9 part 2 where Phoebe is talking to first David and then Mike the shot keeps changing. Each time it does the amount of hair down Phoebe's back changes from a little to a lot. (00:23:30)
The One With Phoebe's Rats - S9-E12
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. (00:14:05)
The One With The Metaphorical Tunnel - S3-E4
Continuity mistake: When Chandler is getting relationship advice from Monica and Rachel near the end, the label on the ice cream tub he is holding changes position depending on whether the shot is close up or not. (00:13:00)
The One Where No One Proposes - S9-E1
Continuity mistake: In the scene where Rachel believes Joey has proposed to her at the hospital after having Emma. Ross is talking to Rachel about her saying yes to Joey's proposal. The nurse brings Emma in to breast feed. When the nurse leaves, she closes the door. However, when they shoot back to Joey a couple of times before he leaves the room, the door is open. (00:19:45)
The One With The Rumor - S8-E9
Continuity mistake: The gang confronts Ross over his affair with a fifty-year old librarian when he was younger. If you watch the mirror behind him (in one of the girls' rooms), it changes angles every time the camera cuts between Ross and the rest of the gang. (00:17:40)
The One With The Truth About London - S7-E16
Continuity mistake: In the flashback to London, the dress Monica is wearing is not the same one that she is wearing in the original episode, The One with Ross' Wedding, although one can see that they tried to make it look similar. (00:16:20)
The One Where Phoebe Hates PBS - S5-E4
Continuity mistake: In the opening scene where Rachel is checking the mail and is walking over to Monica's room, she has a pair of pumps on, then once she has walked in on Monica and Monica runs after her to say she was taking a nap, Rachel is wearing a pair of backless high-heeled sandals, then when Joey and Ross come in, Rachel is wearing the pumps again (we see this when Ross says "I had to talk loud because the movie was loud"). (00:00:10)
Continuity mistake: When Pheobe is talking to Ursula's stalker, her hands move places with no time to do so. (00:02:45)
Continuity mistake: Just before Chandler gives Monica the mixed tape, he tries to manipulate a coat hanger into something feasible. He stretches it out and holds it up, saying "Yes, honey, I made it myself," then the camera cuts to another angle as he throws it down. After the cut the hanger is not as stretched as it was before. (00:10:40)
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.