The One With the Sharks - S9-E4
Continuity mistake: When Ross explains to Phoebe about "Vikram" the big dark jewel on her necklace switches repeatedly from hanging at the left side of her neck to the middle, then to the right side and again to the left side again between shots. (00:16:10)
The One With Ross's Inappropriate Song - S9-E7
Continuity mistake: When Ross is holding Emma, the position he is holding her changes.
The One With Christmas in Tulsa - S9-E10
Continuity mistake: When Wendy is coming onto Chandler her hands are at the top of his tie. When the shot changes, her hands are halfway down his tie.
The One With the Male Nanny - S9-E6
Continuity mistake: When Ross says, "Not knowing when to shut up, that's my thing," the amount of pizza he has eaten changes between shots. (00:21:50)
The One With Phoebe's Birthday Dinner - S9-E5
Continuity mistake: Near the start, when Chandler asks if anyone else smokes, a woman with a brown jacket is seen getting a pack of cigarettes out her pocket. The camera cuts and now she has one in her mouth and is lighting it. (00:02:35)
The One With Ross's Inappropriate Song - S9-E7
Continuity mistake: When Chandler turns around and Joey watches the football game, the door to Chandler and Monica's room is open. However, when Joey sees the sex part of the tape in the next shot, as Chandler is about to turn around and the TV screen is visible, the door is shut. (00:14:29)
The One With Rachel's Dream - S9-E19
Continuity mistake: When Rachel is telling Monica about her dream at Central Perk, Phoebe enters and leaves her bag on the couch but it falls. However, in the next shot, her bag is right at her side on the couch. (00:14:40)
The One With The Lottery - S9-E18
Continuity mistake: Joey's thumb on the wishbone changes positions as the camera switches between Joey and Monica.
The One With the Pediatrician - S9-E3
Continuity mistake: Ross' broken finger disappears overnight. It's broken in one scene, not broken in the next scene which takes place on the same or next day.
The One With The Donor - S9-E22
Continuity mistake: In the first scene in the coffee shop Emma is in a carriage beside Rachel. Later on when they come back to the coffee shop Rachel leaves and the baby carriage and the baby are nowhere to be seen.
The One With The Memorial Service - S9-E17
Continuity mistake: In the beginning when Joey tries to spin the ball with his finger, it falls, hits the table and bounces to the background. In the very next shot it is seen falling behind Chandler on the couch.
The One Where Emma Cries - S9-E2
Continuity mistake: When Chandler wakes up and spits out the balloons, his legs change between shots from being crossed to having one foot on the table and back, at least twice. (02:00:00)
The One In Barbados, part 2 - S9-E24
Continuity mistake: At the end of the ping pong scene when Chandler wins, a paddle appears on the floor for one shot then disappears in the next. No-one had time to touch it. (00:44:20)
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.