The One with Mrs. Bing - S1-E11
Continuity mistake: When Joey says to Ross in the hall 'you didn't call and leave your grip size' his arms are folded. In the next shot, his arms are behind his back. (00:10:20)
The One with Mrs. Bing - S1-E11
Continuity mistake: When they are all eating at the restaurant and Mrs. Bing is telling Rachel how to write a book, the amount of food on Rachel's plate changes between shots without her touching it. (00:06:55)
The One with Mrs. Bing - S1-E11
Continuity mistake: In the final scene Rachel passes out copies of her draft for her book. She gives out all her copies and asks for their opinion. However, near the end of the scene after waving her arms around empty handed a copy of her script magically appears in her hands. (00:21:10 - 00:21:45)
The One with Mrs. Bing - S1-E11
Continuity mistake: When Joey asks Ross 'how could you let this happen' in the hall, his sleeves are down to his wrists. In the next shot, they are rolled up. (00:10:25)
The One with Mrs. Bing - S1-E11
Continuity mistake: When Joey shows Ross the photo of his parents wedding, Ross is holding a magazine. In the next shot, the magazine is gone. (00:15:00)
The One with Mrs. Bing - S1-E11
Continuity mistake: While everyone's at the restaurant Rachel dips a tortilla chip into guacamole and gets some on her hand. When Paolo takes a bite from the chip he also eats the guacamole off Rachel's hand while she's still holding the rest of the tortilla chip, but in the next closeup Rachel's hand is empty, then in the next shot the remaining tortilla chip reappears in Rachel's hand. (00:06:45)
The One with Mrs. Bing - S1-E11
Continuity mistake: At the hospital, the positions of the balloons Monica brings change instantly. Note the blue one. Its height changes drastically from below to level with the yellow one. (00:11:30)
The One with Mrs. Bing - S1-E11
Continuity mistake: When Coma Guy asks who Monica and Phoebe who they are, he has his hands lowered on the bed in one shot and raised outstretched in the next. (00:18:30)
The One with Mrs. Bing - S1-E11
Continuity mistake: The way Joey holds the picture of his mum changes between shots. Note his fingers. (00:15:50)
The One with Mrs. Bing - S1-E11
Continuity mistake: The position of Mrs. Bing in relation to the pay phone keeps changing during her conversation with Ross at the restaurant. (00:08:55)
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.