The One With The Cake - S10-E4
Continuity mistake: Near the end, Monica rearranges Emma's stuffed toys in order of size. When you next see them they are jumbled up, then later they return to being neatly lined up again. (00:19:40)
The One Where Ross Meets Elizabeth's Dad - S6-E21
Continuity mistake: When Monica and Chandler enter the apartment arguing about what time they were supposed to meet, Monica has her handbag strap over her right shoulder, and then takes it off. When the shot switches to Phoebe claiming to know what time they said they would meet, the handbag strap is back over Monica's right shoulder, and then she takes it off again. (00:16:40)
The One With The Inappropriate Sister - S5-E10
Continuity mistake: Ross and Joey are discussing Joey writing his own moviel; Ross sits down to begin writing, and Joey places a beer on the table next to him. The large part of the label is facing to the side, but it then switches to facing the front without being touched. (00:06:20)
Continuity mistake: During breakfast, when Joey and Phoebe are talking about driving back, the fork in Phoebe's left hand disappears and reappears. (00:03:55)
The One With The Metaphorical Tunnel - S3-E4
Continuity mistake: When Monica is telling Susan and Carol that Ross used to dress up as a girl, Ross goes over to the table and picks up a drink. When he picks it up it has a cork in it. In the next shot he has the cork already in his hand. (00:20:30)
The One With The Proposal, part 2 - S6-E25
Continuity mistake: At the end when Chandler returns to his apartment, from the outside he opens the door with his right hand. Then it cuts to an inside view and he's opening it with his left hand on the handle. (00:17:40)
The One Where Ross Moves In - S5-E7
Continuity mistake: Chandler and Joey are on their couch thinking about what to do about Ross; when Chandler says "what are we gonna do?", he switches from crossed arms to hands folded in his lap. (00:15:45)
The One With The 'Cuffs - S4-E3
Continuity mistake: Joey's encounter with the encyclopedia salesman is riddled with errors. First, when the salesman is talking about Van Gogh and saying "He painted that," he points to a page that is all text; later, Joey is reading about vomit, and it is at a pont much further on in the book than when the salesman read about vulcanized rubber (which it shouldn't be, given the encyclopedia is alphabetized); finally, when Joey buys the "V" volume, as he opens it he has a $50 bill in his hand, and when the shot changes to show the salesman he is somehow folding and pocketing it without having taken it from Joey. (00:13:00)
The One Where They're Going To PARTY! - S4-E9
Continuity mistake: When Chandler answers the phone and it's Gandalf calling to cancel, Ross is just opening the fridge, but the shot cuts to Chandler with the phone and Ross is putting two beers down on the side next to him - too quick to have got them there from the fridge. (00:05:35)
The One with All the Poker - S1-E18
Continuity mistake: In the scene where Rachel and Ross are playing poker head to head, Rachel borrows $7 from Monica's purse and then puts the purse down on the table. She puts it down on her left hand side but it then switches to her right hand side without her touching it and then back again. (00:22:25)
The One with the Stoned Guy - S1-E15
Continuity mistake: After Chandler walks in on Ross and Joey's dirty talking, Chandler walks towards the door and Joey turns to Ross. In the next shot Joey has turned around and is facing Chandler. (00:13:15)
The One with Two Parts: Part 1 - S1-E16
Continuity mistake: When Ross, Carol and Susan are watching the birth video, Ross has his hand on the fake baby's head. In the next shot his hand is on its shoulder. (00:15:50)
The One with the Stoned Guy - S1-E15
Continuity mistake: When the monkey is hanging off Ross's date's hair, in one shot he is hanging upside down, then in the next he is hanging the right way up. (00:06:35)
The One with the Candy Hearts - S1-E14
Continuity mistake: In the restaurant when Ross asks Carol to join him, his date has her hand with the chopsticks in it up on the table. In the next shot it is gone. (00:14:55)
The One Where Rachel Tells... - S8-E3
Continuity mistake: When Rachel says Ross can be involved as much as he likes, his arm moves from by his chin to in his lap when the camera cuts. (00:11:25)
The One with Mrs. Bing - S1-E11
Continuity mistake: When Joey shows Ross the photo of his parents wedding, Ross is holding a magazine. In the next shot, the magazine is gone. (00:15:00)
The One Where Ross Dates a Student - S6-E18
Continuity mistake: When Monica is standing in front of Phoebe, asking if the smell from Joey's is bothering her, the shots of Monica from the front show her arms held out in front of her, but when the shot changes her arms are crossed. This happens twice. (00:11:15)
The One With Phoebe's Birthday Dinner - S9-E5
Continuity mistake: When Pheobe says "One really does have a stick up one's ass," the waiter's hands move from in front of him to behind his back. (00:08:05)
The One With The Apothecary Table - S6-E11
Continuity mistake: When Janine goes into the hallway to apologize to Monica about her behavior at dinner, she runs into Monica who says, "What did I tell you about the hall?" As she says this, she is pointing her right forefinger at Janine and her right shoulder is leaned in closer to her. When Janine says "I was just coming over here to apologize for my behavior," the camera cuts to Monica, who is now standing with her left shoulder leaning in toward her. The camera cuts back to Janine as she says "I'd really like it if we could be friends" and then back to Monica for her next line, where she again has switched to her right shoulder leaning toward Janine. (00:19:20)
The One Where No One's Ready - S3-E2
Continuity mistake: When Ross asks Chandler "you took his underwear?", the angle changes halfway through the line. Chandler's hands go from in front of him to being in his pockets. (00:10:50)
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.