Revealing mistake: When the neighbors fall onto the floor of their bedroom when Clark's Christmas lights finally go on, you can tell a stunt double is standing in for the female neighbor as she falls down at the foot of the bed.
Continuity mistake: When the squirrel is being chased by Eddie's dog, it passes through the broken door and then vanishes. (01:22:07)
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: After the squirrel lands on the coffee table, it rises up and twitches its tail in a mechanical motion, showing it is really a puppet.
Continuity mistake: As the shots quickly change from the front of Catherine and Rusty to their backs, Catherine is either holding Rusty tightly to her, loosely, or not at all.
Continuity mistake: When Clark falls off the roof, the staple gun goes down before him. In the next shot, it's not heading down from his point of view.
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: As Clark is stapling the Christmas lights to the house, there are bits of snow and ice on his left-hand glove in the close-ups. But in the longer shots of Clark, the glove has no snow and ice present.
Other mistake: Up in the attic when Clark finds the videos, the video he watches is labelled Christmas '59 but while watching it, the sign being held up says "XMAS 1955"
Suggested correction: It may be a 2nd film he watched after the 1959 film. This may not be in real time, just like we only see Clark in the attic for a few min but in reality the family was gone assumingly much longer than we saw on film and Clark was there longer than we see.
Continuity mistake: After Clark dedicates the Griswold Family Christmas tree and it expands, Ellen's hands are on her hips, but the next quick shot of her shows her hands clasped behind her back.
Continuity mistake: After Clark cuts the rope restraining the tree branches, Rusty is very close to the tree, but the final shot when Clark gives the "OK" sign shows Rusty about two feet from the branches.
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.
Revealing mistake: When Snots the dog chases the squirrel into the Griswolds' dining room, he barely brushes a high-back dining chair that immediately falls on its side. If you look closely, a string attached to the the right side top of the chair can be seen tightening which then pulls the chair down.
Continuity mistake: In the scene of Clark standing in the snow trying to figure out why his Christmas lights did not work, the paper he is holding in his right hand is mid torso to him, but in the next shot when Rusty leaves him, his right hand has instantly dropped to his side and he raises his paper-holding hand again.
Continuity mistake: When Clark, Eddie, and Catherine are admiring the Christmas lights of the Griswold house, Clark is very close to Eddie with his left arm draped over Eddie's shoulder, but the next quick cut to Clark when he says, "Eddie?", shows Clark further away and his left arm at his side, and not stretched out.
Revealing mistake: The stunt double for Nicholas Guest is obvious after Julia-Louis Dreyfus punches him. The hair style of the stunt double is different from Nicholas Guest's hair, which is heavily slicked back.
Continuity mistake: In the Christmas dinner scene, closeups of Rocky show his right hand raised to his face, but the overhead shots do not.
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.
Continuity mistake: After the tree burns, Rusty says, "Dad's gonna flip out." Clark Sr.'s left elbow is close to and behind Rusty's head, but in the next instant shot of Rusty, Ellen, and Audrey, Clark Sr.'s elbow is not there.
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)
