Revealing mistake: When Tim Allen startles Santa Clause and he falls off of the roof, Santa's foot kicks up a blanket that was used to look like some snow on the roof. (00:14:10)
Revealing mistake: When Tim Allen is looking at the reindeer, one reindeer's ear moves. At this point you can see the metal robot in the base of the ear.
Revealing mistake: When Santa slips on Scott Calvin's snow-covered roof, you can see the "snow" wrinkle as he slides.
Revealing mistake: When the elves are tying up the police officer at the station, they do so in a really quick manner. The film here is obviously sped up. You can tell this by the fact that the children playing the elves are breathing really fast.
Revealing mistake: When the original Santa falls off the roof, the path he slides is already visible before he falls, especially in the point of view shot.
Chosen answer: Even though Charlie did not want to stay with his Dad for Christmas Eve, he did want to stay at home with a family member, fragmented as it was. Eating Christmas Eve dinner at a Denny's restaurant was not his idea of a Christmas dinner at home with family.