The One With Rachel's Assistant - S7-E4
Continuity mistake: In the scene when Joey is talking to the producers of Mac and Cheese, he says, "We're not even shooting them anymore?!" As he says this he lifts his left arm up, but in the very next shot his left arm is back down by his side. (00:14:40)
The One With All The Wedding Dresses - S4-E20
Continuity mistake: When Chandler tells Joey that he should go to a sleep clinic, Monica puts her coffee cup on the table, but then it reappears in her hands and disappears repeatedly. (00:02:00)
The One Where Chandler Can't Cry - S6-E14
Continuity mistake: In the previous episode Monica had a very bad cold. This episode carries on immediately after the end of the last one (Monica's still in her dressing gown from earlier), but Monica isn't coughing or sneezing at all anymore. (00:00:05)
The One with the Thumb - S1-E3
Continuity mistake: When Phoebe visits Lizzie, Lizzie is feeding the pigeons with her right hand. In the next shot, a plastic bag has appeared in her left hand from nowhere. (00:11:40)
The One That Could Have Been, part 1 - S6-E15
Continuity mistake: In the scene where Joey gives Chandler the orange juice and says sorry, the paper cup's logo faces Joey's hand, then the shot goes to Chandler and when it comes back, the logo on the cup faces Chandler. (00:15:15)
The One Where Joey Dates Rachel - S8-E12
Continuity mistake: When Ross arrives at the classroom late and out of breath, he tosses his jacket at the hook, but it falls to the floor, and he walks behind the desk anyway. In the next wideshot of the class, as Ross still stands behind the desk, the coat is up on the hook. (Viewed on broadcast TV as a rerun, so there may be a missing shot that was removed for extra commercial time.). (00:07:05)
The One With The Tiny T-Shirt - S3-E19
Continuity mistake: Ross is over at Chandler and Joey's looking through the peep hole for hours waiting for Rachel to return. When she does and Ross sees her go inside with Mark, Ross tries to open the door to go see her, and Chandler jumps on his back to stop him. As Chandler says "I...am not going to let you do this", Ross grabs the door handle. Then the angle changes, and as Chandler says "You...are surprisingly strong," Ross is further from the handle and grabs it again. (00:13:15)
Continuity mistake: In the previous episode, Ross rings the helpline of the makers of the pen and is told the pen won't come off. Yet in this episode it vanishes from Ross and Rachel's faces between getting up and going to breakfast. (00:02:25)
The One Where Emma Cries - S9-E2
Continuity mistake: When Ross and Rachel are talking about which muffin she wants, her sleeves move up and down her arms with the different shots. (00:04:45)
The One Where No One's Ready - S3-E2
Continuity mistake: In the scene where Chandler sits on Joey in an attempt to regain possession of his seat, the shirt sleeve on his left arm becomes unrolled and slides down. When he stands up, the camera cuts to face Ross while he is giving out directions, leaving Chandler's back to the audience. Chandler's sleeve is now rolled back up. The sleeve remains rolled for the rest of the sequence. (00:06:30)
The One Where Monica and Richard Are Just Friends - S3-E13
Continuity mistake: When Richard sits in Monica's room, when Monica opens the door we can see in the background the living room's window draperies, table, picture frame, etc., but they're not as they should be. In this mock-up the shade is pulled down, the draperies look different, and the direction they're all facing differs. (00:15:55)
The One With The Proposal, part 2 - S6-E25
Continuity mistake: When Monica is in Richard's apartment she gets all worked up, so Richard gives her a hug to calm her down. She goes into the hug with her arms curled up in front of her face, but when the camera angle changes, they are at Richard's back. (00:13:50)
The One With Chandler In A Box - S4-E8
Continuity mistake: In the episode with Chandler in a box, when Rachel is showing Ross all the things she had kept from their relationship in a shoe box, her hair is tucked behind her ear in most shots, but when she says "I keep the gifts that matter", it's all loose, then goes back to how it was in the following shot. Also in the shot before that line she's pointing the horn fossil's tip at Ross, but when it cuts to a front view she's holding the horn's tip and pointing the broken end. (00:16:30)
The One With The Baby Shower - S8-E20
Continuity mistake: In the one with Rachel's babyshower, Monica needs to ring Rachel's mom to invite her. She says that she has her number in her phone book and walks over to the phone - we see her start to look at it, but when the angle changes she's got the phone and is dialling. (00:01:00)
The One With The Girl From Poughkeepsie - S4-E10
Continuity mistake: In the scene on the train, when the conductor announces Montreal, Ross's head goes from laying on his shoulder to a upright position from one shot to the next. (00:19:00)
The One With The Tiny T-Shirt - S3-E19
Continuity mistake: When Joey and Kate are talking for the first time, a man walks behind Joey and sets down a chair. In the next shot it is gone, and then it is back again. (00:04:30)
The One With All The Jealousy - S3-E12
Continuity mistake: When Monica is confronting Julio about the poem, there are two bottles upside down on the top of others. He turns one over, but in the next shot there are still two upside down, and then there are none. (00:15:35)
The One With All The Candy - S7-E9
Continuity mistake: When Phoebe sits on the swing (when learning to ride her bike), her scarf has one end down her front and the other over her left shoulder. In the next shot, the end is over her right shoulder instead of her left. A couple of shots later, it is switched back again. (00:11:05)
The One Where Estelle Dies - S10-E15
Continuity mistake: When Rachel walks in with Emma, Ross is on the laptop. It is straight and on the table, in a later shot,the laptop has moved and is over the edge of the table. (00:18:50 - 00:20:55)
The One With The Mugging - S9-E15
Continuity mistake: When Phoebe is talking to Ross about mugging her and he is reading the paper, it changes several times from being folded over to regular size to being folded over again. (00:19:00)
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.