The One That Could Have Been, part 2 - S6-E16
Continuity mistake: When Phoebe is in the hospital bed and Monica gives her a cup of herbal tea, Phoebe is shouting at her for putting honey in it. As the shot changes back and forth the spoon in the cup changes position. (00:02:00)
The One Where Ross Dates a Student - S6-E18
Visible crew/equipment: When Joey walks into Chandler's apartment, Chandler is sitting on the couch talking on the phone. Two microphones are visible. (00:06:20)
The One Where Paul's The Man - S6-E22
Continuity mistake: When Rachel and Paul are on the couch at the cabin, the diet coke Rachel is holding switches (repeatedly throughout the scene) from her left hand to her right. (00:12:00)
Continuity mistake: When Ross and Rachel are in bed, and Rachel says she remembers laughing a lot, and Ross says "Then we didn't have sex," Rachel turns her head away from Ross twice. (00:03:10)
The One Where Ross Dates a Student - S6-E18
Continuity mistake: When Chandler, Joey and Ross are talking about Donna Keystone from college, Ross is holding a water bottle; it disappears, then he is holding it again. (00:13:15)
Audio problem: Right after Ross and Rachel leave the wedding chapel, Joey and Phoebe rush in. Joey is saying "C'mon, Pheebs, hurry, hurry." and she is saying "Okay, okay." However, neither one is moving their lips. (00:00:25)
The One With Joey's Porsche - S6-E5
Visible crew/equipment: Anytime we see the Porsche, there is always a stage light above it. (00:03:30)
The One With The Apothecary Table - S6-E11
Visible crew/equipment: When Joey and Janine come back from the second double date with Chandler and Monica, just as Joey closes the door the end of the set wall and soundstage can be seen at the right side of the screen.
The One With The Routine - S6-E10
Visible crew/equipment: Just as Phoebe walks into the apartment with the duck and chicken (to help find Monica's hidden presents), a crew member's leg/foot can be seen at the bottom left side of the screen.
The One Where Ross Hugs Rachel - S6-E2
Other mistake: When Monica's trying to evoke some kind of an emotional reaction from Rachel, who's polishing her toenails, there's a bottle of Cutex nail polish remover on the table with part of the brand name painted black, so it reads "Cu Ex" on the label.
The One With The Routine - S6-E10
Visible crew/equipment: As soon as Janine gets up to leave the coffee house, a bright stage light with a camera and camera man right below it can be seen. (00:04:00)
The One Where Chandler Can't Cry - S6-E14
Continuity mistake: In this episode Chandler says he can't cry, but in series 4 when he broke up with Kathy he was seen crying, and other times - it's just this episode it's apparently an issue.
Continuity mistake: In the beginning in the coffee house, Ross is explaining to Phoebe and Rachel what 'Unagi' is. The blonde lady behind Phoebe is wearing light blue jeans. She then puts a brown leather jacket on, however in the next shot it has gone, only to reappear and disappear again. (00:03:20)
The One That Could Have Been, part 1 - S6-E15
Revealing mistake: In the opening credits for both parts, fat Monica jumps on the couch and it lifts up on Chandler's end. If you look carefully at Chandler, you can see him holding one end of the couch with his hand and pressing up with his foot. (00:02:10)
The One With Joey's Fridge - S6-E19
Continuity mistake: When Joey pushes Ross against the fridge, a box falls from the top of the fridge onto the shelf beside it. A few seconds later when Joey turns to Chandler, we can see over his shoulder that the box is back on the fridge. (00:08:55)
The One With Joey's Fridge - S6-E19
Continuity mistake: The handle to the fridge door is on the left, so when it opens the inside is visible. In earlier episodes the handle was on the right and it opened out towards the room, blocking the inside from view. (00:00:05)
The One With The Apothecary Table - S6-E11
Continuity mistake: The red eraser knob on the magnadoodle changes from one side to the other, when Janine is going out to tell Monica she is sorry. (00:18:00)
The One Where Ross Got High - S6-E9
Continuity mistake: When Ross finishes the trifile, a small amount of whipped cream appears and disappears throughout a few shots. (00:16:35)
Revealing mistake: When Joey and Phoebe are driving back, the outside is obviously a projection. (00:10:15)
The One With The Ring - S6-E23
Continuity mistake: When Rachel is talking to Monica about Paul crying, just before Rachel leaves, Monica has her hair over her left shoulder; the shot cuts and she now has most of her hair over her right shoulder. (00:09:50)
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.