Continuity mistake: Right at the start, the tapes Roz is holding change hands at least twice. Although you can't often see both her hands, you sometimes see one and yet they still switch by the next shot.
Continuity mistake: When Niles brings out the "Hot-Buns," he hands it to Martin who instantly in the next shot, is pulling it out from under him when Daphne comes in. There really wasn't time for him to put it under himself first.
Continuity mistake: Niles has the "hot buns" pads under his right arm and his mittens in his right hand. The next shot shows he already has a mitten on his left hand even though there was not enough time for him to put it on. (00:10:25)
Continuity mistake: Martin opens the jewel case-like box twice in two different shots in the background. (00:09:55)
Chosen answer: The turkey's stuffing.