Goofs

As Snots the dog is chasing the squirrel through the house, they run over the top of the dining table. The food, plates, and silverware get scattered. A moment later, Clark is walking past the hallway leading to the kitchen with the table visible in the background. The tablecloth and setting are completely undisturbed.

The newel post at the top of the stairs that Clark cuts off with a chainsaw reappears when the guests run upstairs to escape the squirrel.

The police cars speeding to the house were all Ford. Later, when scenes are shown with police cars parked in the background, they are all Chrysler.

When Clark is polishing his sled, the bottom is smooth, but when it is going through the forest there are fins on the bottom.

From the interior of the house, the attic ladder is shown as a slide-down, but from the attic, it has a fold-out design.

When Clark first turns on the Christmas lights, the shot from the power company has the word "Auxiliary" spelled incorrectly.

Clark Griswold's Ford Taurus station wagon is shown to have exterior wood paneling, an option that was never available on this car. (However, it's possible the exterior appliques were added by the filmmakers as a nod to the "Wagon Queen Family Truckster" the Griswold family bought in National Lampoon's Vacation (1983)).

Clark informs Eddie that the sewer is a storm run-off sewer, implying that the waste material Eddie is pumping into it will not be treated; additionally, with the absence of precipitation or significant melting, Eddie's chemicals remain stagnant until the end of the film. In reality, Chicago has a single, unified sewer system; storm run-off and wastewater run through the same mains for processing by the MWRDGC and the mains are therefore constantly flowing with effluent.

When Clark is walking around in the attic, he continually walks beneath the slats which would have immediately resulted in him going through the sheet rock and punching a hole in the ceiling.

The family Christmas tree shrinks smaller and smaller throughout the movie. This could be because they trimmed it back considerably so it didn't take up the whole room.

In one scene after all the parents have come to the Griswold home for the Christmas holidays, they are all seen sitting watching the Macy's Thanksgiving Day Parade. This parade occurs in late November not the middle of December.

This could have been an encore presentation, or a VHS recording of the parade.

When Clark is locked in the attic, he sees a movie reel marked "Christmas 1959" but when he's later watching movies, it says "Christmas 1955." However, there might have been several years worth of Christmas movies, and the first one we see him watching wasn't necessarily the first reel he looked at in the box.

When Clark says he wants his boss "brought here" to confront him about his Christmas bonus, Eddie leaves to go and get him. Eddie is visiting from Kansas. How did he know where to go to find Clark's boss? Clark mentioned "Melody Lane" but didn't give the exact address.

Eddie could easily have looked up his address in the phone book, or in company documents Clark surely has in his home.

Clark says he has 25,000 lights on his house. These are the old-fashioned bulbs that draw 7 watts each; thus, Clark would be drawing 175,000 watts of power, or 175 kilowatt (kW) continuous draw, far more than can be delivered to a single-family dwelling using the U.S. standard 120/240-volt electrical system. Therefore, Clark's main breaker would have instantly tripped the second he would have plugged in all the lights at once, not counting the lights on his Christmas tree and everything else electrical in his house.

This is an obvious piece of artistic license done for comedic effect.

Right before Clark goes to try out the lubricant that is "500 times more slippery than cooking oil," the pyrotechnic line that Clark takes can be seen going down the hill before it ignites.

A tow rope is visible pulling Clark's sled.

When Clark gets trapped in the attic, skylights are visible; yet from the outside of the house, they are gone.

When Eddie leaves Frank's mansion, the "snow" in the driveway wiggles.

When the SWAT team arrives to rescue Mr. Shirley, the entire Griswold house is dark, yet the whole family is inside with all the lights on but they are not shining through any of the windows. Even when the SWAT team breaks through the windows they are dark, yet the second they arrive inside the house, it is still well lit.

When Ellen cuts a head of cabbage in half after her mother asks her if she's smoking again, the sound of the knife hitting the cutting board is heard before the knife touches the cabbage.

Clark uses a mechanical stapler to put up the lights on the house. The sound of the stapler is that of a power stapler that is powered by an air compressor.

When Clark is sledding down the hill, he passes a school bus. The school bus has the sound of a Doppler truck horn, rather than a school bus horn.

About midway through Clark's rant, a crewperson's head dips into the bottom left corner of one of the long shots.

Several shots show the dining room has no ceiling, but rather a grid of beams.

After Clark cuts the Christmas tree and the tree expands to its natural size, the second tree limb to break through the window has a 2x4 attached to it. This must have been used to push the branch through the glass.

Just before Clark takes off down the hill in the sledding scene, there is a shot looking down the hill where you can clearly see the wires/cord in the snow that are used to make it look like the snow flies in the air as the sled races down the hill.

When Clark is getting his coffee in the office talking to his co-worker, the crew is reflected in the coffee pot.

The Christmas tree trip shows small mountains in the background and log-hauling trucks on the highway, neither of which accurately represent an Illinois landscape.

Due to being partially being filmed in Burbank, one can occasionally spot California vegetation in the background, such as ivy climbing telephone wire and Southern California coniferous trees.

When Ellen and Clark are outside alone trying to light the Santa, a "wet-barrel" fire hydrant that cannot possibly be used in Chicago due to freezing is visible. This type of fire hydrant is found in Southern California where there is no chance of freezing.

Cousin Eddie, upon describing his true plight to Clark, proclaims that the "Gas money give out in Gurnee." It is strongly implied that Eddie and the family traveled from the state of Kansas as it is clearly stated during the kidnapping scene that his RV has license plates from there. The city of Gurnee is 40 miles north of central Chicago. There is not a single viable route from Kansas to Chicago that goes through the city of Gurnee.

When Clark cuts down his own pine tree in the front yard, the way the tree fell through the neighbor's window implied the tree was in the rear yard.

When the Christmas lights go on by accident the first time, their extreme brightness is enough to cause the obnoxious neighbors to shut their eyes even though they are indoors and not looking directly at them. Yet Ellen is in front of the house and looking right at them yet experiences no blinding effect.

When the attic ladder slides down it hits Clark in the mouth and jaw. When he's climbing into the attic in the next shot he's rubbing his forehead.