The One Where Joey Moves Out - S2-E16
Continuity mistake: When Joey and Chandler are at Joey's colleague's brunch, you can see a big wall clock in some shots. You can see it when Chandler says: "Wow, there's my fantasy's come true" with the minute hand at five to the hour. Just a few seconds later, when Joey says: "Can you see me in a place like this?" it can be seen when Chandler is in shot, and the minute hand is now at 20 to the hour. (00:05:40)
The One With Joey's Interview - S8-E19
Continuity mistake: In the opening scene Rachel is holding a white felt pen in her hands and gesturing with it while she talks about the soap opera digest magazine. Between shots the pen sometimes has its cap on and then it's off again so you can see the blue tip. (00:00:20)
The One With Ross's Wedding, part 2 - S4-E24
Continuity mistake: Joey is in their hotel room asking Chandler where Monica is, and the open bathroom door behind Chandler alternates from wide open to halfway open between shots.
Continuity mistake: When Rachel tells Ross that she is still in love with him, her hair keeps changing from behind her ear to down when the camera changes angles.
The One With Rachel's Going Away Party - S10-E16
Continuity mistake: When Ross fears that Rachel is going to talk with him, the volume and the color of his beer changes between shots.
The One With Ross's Library Book - S7-E7
Continuity mistake: When Monica says, "She has beaten me, Chandler, I'm tired," she puts her hands on him and they are in fists, then they are flat out, then in fists again.
The One With The Donor - S9-E22
Continuity mistake: When Phoebe enters the coffee house to get Joey's advice on her outfit for Mike's sister's party, it cuts to Joey saying "You look stop-eating hot", and Phoebe's left hand can be seen making a nervous up-down motion in response. But when it cuts back to her, it is her right hand making the motion and her purse is now in her left hand.
The One With Rachel's Date - S8-E5
Visible crew/equipment: When Rachel and Cash leave Joey's apartment, in the top-left corner a stage light is visible. (00:12:05)
The One With The Cake - S10-E4
Visible crew/equipment: At Emma's birthday party, Joey and Phoebe are discussing the performances they are doing for Emma. The balloons placed behind them reflect the stage and spot lights. This happens throughout the episode in most of the balloons.
The One With Monica and Chandler's Wedding, Part 1 - S7-E23
Revealing mistake: When Monica leaves the apartment and Chandler stays listening to the answering machine, check the wall beside the door. It changes the angle, as if somebody moved it (probably to hide the hall).
The One Where Monica Sings - S9-E13
Visible crew/equipment: When Gavin goes to the door to bring Rachel soup you can see a camera man's microphone in the top of the screen. (00:10:50)
The One With The Birthing Video - S8-E15
Revealing mistake: When Monica gets out of her room to show Chandler her sexy clothing, as she opens the room's door, the buildings from across the street move. The scenario was a curtain and the wind that the door made when she opened it on the set made those curtains with the buildings printed in move. (00:06:25)
The One With Monica and Chandler's Wedding, Part 1 - S7-E23
Revealing mistake: When Monica leaves her apartment in the scene where she thanks Chandler for staying calm since they got engaged you can see the wall on the left side of the door moving as the door closes.
The One With The Bullies - S2-E21
Continuity mistake: When the fight scene starts, one of the bullies takes off his watch and puts it into his right jacket pocket. When they put all of their jewellery into his cap, he gets his watch out of his right jeans pocket.
The One Where Chandler Doesn't Like Dogs - S7-E8
Continuity mistake: When Rachel and Tag are on the balcony and Tag says, "What did Joey say? I like you back?" he is standing on the balcony with one hand in his pocket and the other in front of him. As the camera angle changes, Tag is now in a different position, with both his hands behind him, leaning against the balcony before he moves forward.
The One With Princess Consuela - S10-E14
Visible crew/equipment: At the very start when Monica mentions swinging, all the stage lights are visible in her glass of red wine. (00:00:20)
The One With Ross's Wedding, part 1 - S4-E23
Other mistake: When Phoebe tells Rachel that she thinks she can help her get over Ross, she starts by saying that she needs some photos of Ross. Rachel immediately starts walking towards the kitchen, walking right past the red box of photos on the table beside Phoebe (which she will pick up on her way back and then hand to Phoebe), before Phoebe even mentions the chocolate (and then glass of water) she also needs. It's obvious that Rachel is headed for the kitchen before she knows she needs to go there. (00:12:00)
The One With the Pediatrician - S9-E3
Visible crew/equipment: When we first see Joey and Mike at the restaurant we can briefly see a boom mic above them. (00:08:25)
The One With The Vows - S7-E21
Visible crew/equipment: When Monica and Chandler are in the coffee house after they've finished their vows, there is a microphone and another piece of equipment moving outside behind Chandler. (00:19:40)
The One With Joey's Award - S7-E18
Continuity mistake: When the student is telling Ross he is in love with him, Ross arms are crossed one way, and in another shot they are crossed another. (00:04:00)
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.