The One With The Chicken Pox - S2-E23
Continuity mistake: When Phoebe and Ryan are playing Monopoly, she rolls the dice and one goes off the board (but stays on the table). It then cuts to a wider view of them and both dice are back on the board. (00:09:50)
The One With The Chicken Pox - S2-E23
Continuity mistake: When Monica says about Richard not having a 'thing', her arms change place depending on the shot. (00:14:10)
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.