Continuity mistake: When Chandler and Monica are in the birthing room and they have just been told they are having twins, her scarf keeps changing from sitting on her shoulder to being over her shoulder. (00:10:20)
The One Where the Monkey Gets Away - S1-E19
Continuity mistake: When Monica looks at Barry and Mindy's engagement notice in the magazine, she folds the page over. In the next shot, the magazine is open in her hands. (00:01:50)
The One with the Stoned Guy - S1-E15
Continuity mistake: After Chandler walks in on Ross and Joey talking dirty, Ross is holding his right hand up as he and Joey start to explain to Chandler. In the next shot his arm is by his side. (00:13:10)
The One with the Candy Hearts - S1-E14
Continuity mistake: Just before Carol and Susan enter the restaurant, Ross reaches for the menu with his left hand and his right hand is under the table. In the next shot his right hand is holding onto a cup on the table. (00:11:20)
The One with the Boobies - S1-E13
Continuity mistake: After Phoebe tells everyone she broke up with Roger, Monica has her legs crossed and Rachel has them uncrossed. In the next shot, Monica's are now uncrossed and Rachel's are crossed. (00:20:50)
Continuity mistake: When Joey and Chandler are discussing Joey's shoes, the length of the sleeve round Joey's neck changes depending on the shot. (00:11:20)
Continuity mistake: When Monica and Rachel are discussing Phoebe, Rachel's hands go from playing with the table to dry washing depending on the shot. (00:12:30)
The One with George Stephanopoulos - S1-E4
Continuity mistake: After Rachel speaks to her pregnant friend, they manage to swap places between shots. (00:05:50)
The One with the East German Laundry Detergent - S1-E5
Continuity mistake: At the start of the episode when Ross says, "Multiple orgasms", you can see Chandler's boot is not resting on his knee. In the next shot it has appeared from nowhere. (00:00:55)
The One With Joey's Big Break - S5-E22
Continuity mistake: When Rachel knocks over the cereal its position changes between shots. (00:04:15)
The One In Barbados, part 2 - S9-E24
Continuity mistake: At the end of the episode, when Joey walks into Rachel's hotel room, he is standing in the doorway. However, when Joey and Rachel kiss, there is enough space for the door to close. (00:47:05)
The One With The Rumor - S8-E9
Continuity mistake: When Rachel is offering Will the yams, the spoon that's in the dish is facing Rachel. When the shot changes to Joey lifting up the Turkey, the spoon is suddenly on the other side of the dish and facing towards Will. (00:11:05)
The One Where Chandler Crosses The Line - S4-E7
Continuity mistake: When Cathy and Chandler are talking while sitting inside the boat, the silver object on the corner of the counter behind Chandler disappears between shots. (00:08:20)
The One With Rachel's New Dress - S4-E18
Continuity mistake: When Rachel shoos the birds into the hall, the chicken turns around and heads away from the guys' door, however when Joey opens the door the chicken is right outside the door. (00:10:15)
The One Where They All Turn Thirty - S7-E14
Continuity mistake: When Monica is at the party and she is drunk, there is one point when she is sitting down on a chair with Chandler on her right. Chandler is holding her left hand (which has a snack in it), but when it cuts to a front view of Monica, suddenly both her hands are on her lap. (00:13:45)
The One With Joey's New Brain - S7-E15
Continuity mistake: When Joey is talking to the woman whose brain he receives, as the shot changes she is holding a glass, then a cigarette then a glass again, with no time to change objects, let alone anywhere to put the other. (00:06:05)
The One With The Home Study - S10-E7
Continuity mistake: When Phoebe and Mike first donate the money to the children, the way the man is holding the cheque changes depending on the shot. (00:03:15)
The One with All the Poker - S1-E18
Continuity mistake: When Rachel finds out she has an interview she is holding the letter in her left hand. When the shot changes, the letter is in her right hand. (00:09:05)
The One with the Boobies - S1-E13
Continuity mistake: When Phoebe's boyfriend is talking about Chandler at the coffee shop, the cookie he is holding jumps from his left to his right hand in an instant between shots. (00:03:20)
The One with Mrs. Bing - S1-E11
Continuity mistake: In the final scene Rachel passes out copies of her draft for her book. She gives out all her copies and asks for their opinion. However, near the end of the scene after waving her arms around empty handed a copy of her script magically appears in her hands. (00:21:10 - 00:21:45)
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.