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.
Visible crew/equipment: When Eddie and Clark are putting the burned chair in the garbage, you can see the shadow of the camera following them.
Continuity mistake: When Rocky runs out of the RV and stands in front of his mom, her mittened right hand is on his shoulder but in the next shot it's not.
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.
Visible crew/equipment: Just as Clark begins his explosive argument, there is a shot of the family watching in horror, and the top of the set is visible at the top of the frame.
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.
Factual error: When Clark is sliding on the saucer, he shoots out a shower of sparks when he crosses the street. Those old saucers were made of aluminum, and aluminum can't create sparks like other metal does.
Visible crew/equipment: When Ellen opens the door after Clark falls from the tree, there's a strange white thing visible for a few frames at the upper left of the door. Might be the hand of a crew member opening the door.
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 Clark and Eddie push the chair to see what happened, the burned cat is only visible in closeups. There's also a blue object next to the couch that look like an iron that is creating the smoke effect.
Continuity mistake: When Clark's neighbours return home, the man says to Clark, "Where do you think you're going to put a tree that big?" The trunk is very large, bigger then Clark's feet. Clark replies, "Bend over and I'll show you." Then Clark cuts the tree trunk - it is very thin and easy for him to cut.
Audio problem: During dinner on Christmas Eve there is a shot of the cat chewing on Christmas lights. The sound of the cat chewing is a fraction of a second off.
Continuity mistake: In the road rage scene with the redneck's pickup truck, the logging truck's trailer is passing the Griswolds' car with plenty of room for their car to fit underneath. However, the next shot before Clark steers under the truck's trailer shows the semi truck's cab just coming abreast of the Griswolds' car.
Plot hole: When cousin Eddie kidnaps Mr. Shirley, Shirley's wife immediately calls the police. She describes Eddie as 'brutish and huge' or something similar, and wearing a 'blue leisure suit'. She also mentions that she got the license plate number of the vehicle. But how did the SWAT Team know to go to the Griswold's house to find Mr. Shirley? Eddie's RV is not registered in the Griswold's name so the plate numbers would not be much help in finding the culprit.
Continuity mistake: During Clark's rant, the shot goes from seeing him from behind the whole family to a frontal view of the family looking at him in shock. In the first, they are standing in line with the entrance to the room. You can even see Eddie's shadow on the wall as he's very close and slightly behind it. Also, on the other side, Audrey's arms are going down to her side and she's a little behind Art. In the next shot, there is no wall and Audrey is in front of Art. Her arms are also crossed.
Factual error: Even though this movie takes place at Christmas and there is lots of snow around the outside of the house, you can tell this was filmed during the summertime due to the short shadows in some outside scenes. At Christmas time, shadows are longer all day long.
Continuity mistake: When Clark is stapling the lights to the roof, his leg is tangled in the sting of lights causing him to lose his balance and slide of the roof. As he slides/falls grabbing the gutter the string of lights around his leg disappears.
Factual error: The family is reacting to where Clark went flying down on his saucer, ending up in a Wal-Mart. With the speed and length of the trip, he would've been out of sight in seconds. There was no way that they could see him from where they were.
Continuity mistake: After Eddie's arrival Clark is on the lawn with "Snots." Clark's left had is shown as he is there alone with the dog trying to get his attention and his glove and wedding ring have both disappeared.
Answer: They didn't go to a Christmas tree farm. He took them to a huge forest to get one most likely because it would be easier to get one free then to pay for one.
They went to a tree farm. After running off the road and jumping the snowbank the wagon crashes through a sign that says "Trees." Clark then says, "We're here...and we made good time too." The humor is Clark forgoes a normal "farmed" tree for the "wild" monster he takes home.
False. They may have run over the tree farm sign, but they absolutely did not harvest a tree from the tree farm.