The One With The Halloween Party - S8-E6
Continuity mistake: When Phoebe is talking to Ursula's fiance Eric, he is wiping sweat off his face with a napkin. He puts the napkin to his eye and then in the next shot it changes to the other eye without him having enough time to change it. This happens again when at one point he's wiping his eye and then suddenly his forehead. (00:07:45)
The One With The Halloween Party - S8-E6
Continuity mistake: The amount of carrot Chandler has keeps changing from less to more. (00:10:35)
The One With The Halloween Party - S8-E6
Factual error: This show is set in October (it's a Halloween party). Rachel's stomach is completely flat, but according to the show, she got pregnant in April (It's stated several times by the characters on the show that Monica and Chandler's wedding was in May, and we learn in "The One With The Red Sweater" that she got pregnant a month before the wedding. Hence, April). However, by October she should have a six months' pregnant belly, which is no way resembles the perfectly flat belly she shows.
The One With The Halloween Party - S8-E6
Continuity mistake: When Rachel returns from running after the boy that she told to "shut up", you see Joey picking up a piece of food, sniffing it and making a face and then putting it back on the tray. However in the next shot, without moving, Joey is munching on something - he didn't have anything in his hand before. (00:19:55)
The One With The Halloween Party - S8-E6
Visible crew/equipment: Right after Joey has finished his impersonation of Chandler, kids can be heard knocking on the door. When the camera pans to Rachel, stage lights can be seen in the top right-hand side of the screen. (00:05:15)
The One With The Halloween Party - S8-E6
Continuity mistake: While Phoebe is calling out Ursula for lying to Eric, her hair continuously changes position from behind her shoulder to in front of her shoulder depending on the camera angle. (00:14:50)
The One With The Halloween Party - S8-E6
Continuity mistake: When Chandler and Ross are arguing, the nose on Chandler's costume moves. In one shot it's on his chin. The camera then cuts to Joey and Monica and back, and then it's down round his neck. (00:12:20)
The One With The Halloween Party - S8-E6
Audio problem: When Rachel greets Mona at the door of the apartment, visually she says "Hi" but the audio is " Hi Mona. "
The One With The Halloween Party - S8-E6
Other mistake: When Monica is saying "I can't answer that, Chandler's my husband" after Joey asks her who would win in a fight between Ross and Chandler, the camera is fluttering in and out of focus. (00:11:11)
The One With The Halloween Party - S8-E6
Continuity mistake: When Joey is saying that he doesn't want to dress up, behind him is a guy with his shirt on top of his pants but in the next shot it is down. This happens throughout the whole scene. (00:00:35)
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.