Continuity mistake: At the end of this episode, Ross opens the door of Rachel's room, says "Hi", and then closes it. However, in the next episode (The One With The Jellyfish), this scene is shown again and changed: Ross opens the door of Rachel's room, says "Hi", and doesn't close it - he talks with Rachel and Bonnie with the door open. (00:21:05)
The One Where Emma Cries - S9-E2
Continuity mistake: When Rachel wakes up Emma during a nap, against Phoebe's advice, there is a shot of Emma in the cot. She is wearing a plain pink hat, but in the next shot, when Rachel lifts her out of the cot, she is wearing a white hat with what looks like little flowers on it. (00:05:55)
The One That Could Have Been, part 2 - S6-E16
Continuity mistake: Rachel is talking to Joey in his apartment after waking up the next morning, looking messy and rumpled. As she talks, her bra strap slips down her arm. In one shot (as she says "I'm a horrible person"), the strap is all the way down her arm and then in the next shot it is tucked under her shirt. (00:10:00)
The One Where The Stripper Cries - S10-E11
Continuity mistake: Towards the end of the episode, Ross and Chandler come into Monica's apartment and Ross asks where Rachel is. Watch the objects in Monica's hands, in the shot from behind she puts them on the table, and then does it again in the shot from the front. (00:24:00)
The One With The Blind Dates - S9-E14
Continuity mistake: When Phoebe says that they should not tell Ross that the date is cancelled so that he gets stood up, Joey says, "I hear that's bad" - implying that he has never been stood up so doesn't know how it feels. However, in TOW Two Parts (Part II), Ursula stands Joey up, and he takes it pretty bad. (00:06:40)
The One With Monica's Boots - S8-E10
Continuity mistake: In The One With Monica's Boots, Monica is removing her trainers and replacing them with her boots so it looks as if she was wearing her boots all along. In one shot her left jean leg is tucked into her boots, but when she stands up it is sitting perfectly. (00:07:25)
The One with the Thumb - S1-E3
Continuity mistake: When we first see Chandler in his office, his sleeve is rolled below his elbow. In the next shot, it is above his elbow. (00:12:30)
The One With The Lottery - S9-E18
Continuity mistake: In TOW the lottery tickets series 9 just after Chandler has got the job and he sits down you can see Joey's hand in the right side of the screen however when the shot changes Joey moves his hands up to the position we have just seen. The shot changes back and his hand is in the same position. (00:18:50)
The One with the Blackout - S1-E7
Continuity mistake: Rachel takes the cat to apartment number 8 and Mr. Heckles opens the door. However, in this episode, the girls' apartment is labeled number 5 which means that number 8 is above them. In later episodes, Mr. Heckles always says that the noisy girls upstairs are keeping him from doing things. [It makes a bit more sense later on in the series when Monica and Rachel's appartment changes to number 20, which is when Mr Heckles starts to complain about the noise (although in the flash back episode when Phoebe is still living with Monica it seems apparent that they actually know Mr Heckles, which Phoebe shows no sign of when she and Rachel are looking for the owner of the cat).] (00:13:40)
Continuity mistake: The number on Pheobe's cab changes throughout series 2 and 3. 7E85 and 2X85 respectively.
The One With Princess Consuela - S10-E14
Continuity mistake: When Phoebe sits down in the coffee house and tells Chandler and Monica her new name, she takes her jacket off twice. (00:07:20)
The One With The Rumor - S8-E9
Continuity mistake: When Ross hands Rachel the Yams in order to break the tension, the amount of food on both Ross' and Will's plates changes between shots. Also several wine glasses appear on the table. (00:12:30)
The One With The Fake Party - S4-E16
Continuity mistake: After Rachel explains her plan for the fake party, just as Emily opens the apartment door the message written on the Magna Doodle reads "Joey enjoys the," but when Emily and Ross are standing in front of the door the message reads "Joey eats little."
The One With The Embryos - S4-E12
Continuity mistake: At the end, when Monica asks about the garbage bags the apartment's front door is closed, but when Rachel opens the drawer and freaks out about what's inside, the front door is wide open (for the camera) as she kicks the drawer shut, and then the door is closed again. (Widescreen).
The One Where Monica Gets a Roommate - S1-E1
Continuity mistake: While Joey and Chandler are at the apartment with Ross, a watch suddenly appears on Joey's wrist when he announces that he and Chandler are done with the bookcase, then the watch vanishes and reappears again in the following shots at the apartment. (00:15:40)
The One With Rachel's Book - S7-E2
Continuity mistake: When helmet-wearing Vicar Joey taunts Rachel one too many times she turns the tables on him, so when Joey backs away from Rachel he gets pushed up against the front door, and although he can't move, in the shot facing Joey he's at the left side of the door, but in the side shots he's at the right side of the door.
The One With Mac & C.H.E.E.S.E. - S6-E20
Continuity mistake: After Chandler has written the message on the Magna Doodle, the sliding eraser moves from the right to left side just as he leaves with Monica, and when Joey and Chandler are playing foosball, the barely legible "Joey" is now neatly written on the Magna Doodle, and its sliding eraser is again back to the right side.
The One Where Chandler Can't Cry - S6-E14
Continuity mistake: When they're watching the vampire video, Monica, Chandler, and Rachel are sitting on the couch, but in the closeups of the TV we can see the couch in the reflection and it's empty.
The One In Vegas, Part 1 - S5-E23
Continuity mistake: After Joey tells Chandler about his identical hand twin and plans for getting rich, when he sees Chandler's reaction Joey asks, "Are you unsupporting me again?" while he lifts his left arm and points accusingly at Chandler, but next shot it's Joey's right arm that's up and pointing.
The One With Rachel's Other Sister - S9-E8
Continuity mistake: When Rachel tells Amy that she'll let her use the Ralph Lauren discount Amy hugs her, and the glass Amy's holding in her left hand switches to her right hand and then back to her left hand, between shots.
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.