Character mistake: When the National Anthem is sung at the end the uniformed police officers should be at attention and saluting. The Lieutenant holding his hat over his heart is totally incorrect. Police and military in uniform keep their hats on, stand at attention and salute. It is correct for Eddie, as a veteran, to render a salute. It's kind of hard to hear, but it sounds like the 2 dads were arguing at breakfast about eating K rations, so one or both probably served in WW2. As vets, they should have also saluted, although it is not mandatory. For the uniformed on duty police it is. (01:32:53)
Revealing mistake: When Lewis's coat catches on fire after the Christmas tree explodes, the square on his coat that holds the "fire" is evident.
Continuity mistake: When they first step up to the tree in the forest, Audrey is still moving. In the overhead shot, she stops, and we can see tracks in the snow where all four have been standing. The problem is, there are a lot of tracks. We're lead to believe they just walked up to the tree.
Continuity mistake: After Mr. Shirley tells Clark he will get a bonus plus twenty percent, Catherine, Rocky, and Ruby Sue cheer and get up from the couch to mingle with the relatives while Rusty and Audrey respond excitedly. There is a close up reaction shot of Clark as he begins falling, then a long shot of Clark falling to the floor as Catherine, Rocky, Ruby Sue, Audrey and Rusty are in their original positions on the couch, calmly watching Clark fall.
Other mistake: After we see the cat pulling on the strand of white Christmas tree lights, there is a close up shot of the electrical outlet with one cord plugged into it. When the lights go off, both the colored and the white lights go out at the same time. Clark has to plug in two cords to make both sets of lights come back on. Either the colored lights should have been out to begin with, or both strands of lights should have come on with one plug. (01:09:05)
Continuity mistake: When the family is on the front lawn to inaugurate the Christmas lights, between shots a blue Lincoln at the curb disappears and a station wagon appears across the street.
Continuity mistake: When Eddie and Clark are drinking eggnog, Eddie knocks down the decoration with propellers on it. When Eddie walks to the table with the nuts on it the camera shots cut from Eddie to Clark attempting to fix the decoration. In each shot that we go back to Clark, the number of propellers left on the decoration change even after Clark has given up fixing it. (00:45:55)
Revealing mistake: When Julia Louis-Dreyfus has the dog jump on her, you can tell it's a stunt double. In the shot of Julia, the gem on the back of her sequence dress and her hair doesn't go below the gem. When Snot is about to jump on her, the hair completely covers the gem and is much fuller and looks like a wig.
Other mistake: When Clarke and Eddy are drinking eggnog by the tree, and Snots is drinking the tree water, look at the tree's trunk. It's a birch tree not a pine.