The One With The Fertility Test - S9-E21
Continuity mistake: When Rachel takes her gift certificate to the massage parlour to claim her free massage, she hands it to the receptionist and we can see that it has been torn up into eight pieces and taped back together. Yet when Phoebe tears up the gift certificate in a previous scene, we see her tear it into only four pieces before handing it back to Rachel. (00:05:00 - 00:08:20)
The One With The Fertility Test - S9-E21
Continuity mistake: Just before we see Janice, Monica has her hands on Chandlers chest. When it cuts to the wide shot, her hands are round his neck. When Chandler says 'Aw come on.', her hands are on his chest again. (00:12:50)
The One With The Fertility Test - S9-E21
Continuity mistake: When Charlie tells Ross about the Met, Ross goes sitting next to her, and his hands are empty when he says: 'Joey really knows his art, huh?' When Charlie says: 'Not so much' Ross suddenly holds a book in his hands. Then, when the shot changes, the book is gone again. It keeps (dis)appearing during the scene. (00:20:35)
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.