The One With Phoebe's Uterus - S4-E11
Continuity mistake: When Phoebe is on the couch in the coffee house, talking to Monica and Rachel, the puppy moves and the way Phoebe is holding the puppy changes between shots. (00:17:00)
The One With Phoebe's Uterus - S4-E11
Continuity mistake: When Monica is drawing the seven erotic zones, she says there are seven and Rachel says, "Let me see that!" Rachel has one leg on the couch and then in a flash she has them both on the table. (00:14:05)
The One With Phoebe's Uterus - S4-E11
Continuity mistake: At the beginning, Alice and Frank tell Phoebe that they have been trying to get pregnant. When Alice says, "You know, no one's getting any younger", Frank looks at Alice and laughs. In the next shot however, he is looking at Phoebe and doesn't seem to laugh. (00:01:00)
The One With Phoebe's Uterus - S4-E11
Revealing mistake: Phoebe already has a visible baby bump before she even agrees to get pregnant.
The One With Phoebe's Uterus - S4-E11
Continuity mistake: In the scene where Joey is showing kids around the museum, there's a little boy who corrects Joey about the existence of the Mastodon. The kid's arm is by his side at the beginning of the scene. When he begins saying, "Isn't the Mastodon from the Pliocene Epoch?" his left arm is suddenly up and his thumb pointing at the Mastodon. (00:07:05)
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.