The One With the Sharks - S9-E4
Revealing mistake: While Monica and Rachel are talking about Chandler's "jollies to Jaws" Rachel's wearing a colorful flowery top, and after Joey walks in just as Monica takes her seat at the table in the closeup, it's Jennifer Aniston's stand-in, wearing a blue top, who is seated beside Monica. Rachel's hair is wavy in the flowered top, but straight in the blue top (viewed in widescreen). (00:12:22)
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 the Sharks - S9-E4
Continuity mistake: When Chandler and Monica are talking about Chandler's shark obsession, his arms keep changing with each shot. When the shot is from behind (facing Monica) they are on the couch, and when the shot is in front (facing Chandler), his arms are folded in front of him. (00:19:35)
The One With the Sharks - S9-E4
Continuity mistake: In 'The One With The Shark Porn' (Series 9), when Chandler and Monica are talking about his supposed shark obsession, Chandler's collar switches from up to down depending on the shot. It switches several times during the scene. (00:20:30)
The One With the Sharks - S9-E4
Continuity mistake: In "The One With the Sharks", Phoebe talks to Joey about how he's never been in a long term relationship. He has been, though - Angela Delveccio, who he went out with for three years. (00:21:40)
The One With the Sharks - S9-E4
Continuity mistake: After Monica, Rachel, and Joey have been discussing Joey's problem Monica asks him if he thinks sharks are sexy, and when Joey asks about the Little Mermaid it cuts to Monica's closeup and the water bottle cap is on, but in the next closeup of Rachel the cap is off.
The One With the Sharks - S9-E4
Other mistake: While Monica, Rachel, and Joey are seated at the table talking about Joey's problem, there's a Dasani water bottle on the table with part of the brand name painted black so it reads "Asav" on the label.
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.