Immediately before the Family Truckster crashes through the "road closed" in the dessert, Edna can be seen gasping before Clark and Rusty, possibly a cue mistake. Following which, Ellen clearly can be seen laughing as she leans over for cover.
When Clark hooks the dog's leash onto the driver-side back bumper, it actually comes unhooked when the dog dashes at Clark and rests on top of the bumper. In the next scenes, the dog is dragged to his death because of Clark leaving the leash hooked around the bumper.
As the Griswolds are leaving Chicago, the exterior, overhead shots of the Truckster show downtown Chicago, with high-rise skyscrapers in the background. But the "in the car" views show a lower-class industrial area.
Graffiti is spray painted on both sides of the "Family truckster" in one scene, but in the rest of the movie, the spray paint on the driver's side is gone but the graffiti on the passenger side stays throughout the entire movie.
When Clark pulls up the trip route on the TV screen, the line representing their route is shown on the full US map traveling through the state of Oklahoma, but when Clark zooms in to show Day 1, the route line is shown going through Kansas, which would make more sense, since the Griswolds would be stopping to visit Cousin Eddie and his family in Kansas on their way to Walley World.
After the "shower scare" scene, Ellen comes out of the bathroom wearing an unbuttoned pajama top (which she appears to only try to button the top button as she brushes her hair), but in the next shot when she crawls into bed, her pajama top is fully buttoned down.
When they get out of the family "truckster" at Wally World the line of cones is way off to the right but when they start running towards the park they are running right next to them and you can see the car parked in the distance right next to them so the car changed positions.
As Clark and Ellen enter the office, Clark opens the door for Ellen using his right arm. As the view switches to an interior shot of them coming in, Clark is holding the door open with his left hand, with his left arm over Ellen's head.
At the start of the movie when Clark pulls into the car yard in his old car' the shot shows him stopping in the left lane of the yard's slip road. In the next shot however when he gets out, the car is now in the opposite lane and further forward.
As family gets into the truckster to start their trip there is no luggage on top of the car. As soon as Clark puts the car in reverse several pieces of the luggage are stripped of the roof of the car after striking the top of the garage door.
The motorcycle cop orders Griswold out of the car. At that time, the cop
has his sunglasses in his hand. As Griswold is exiting, the exterior shot
shows the sunglasses tucked into the cop's shirt button.
Clark and the Motorcycle Cop are talking in close-up at the rear of the vehicle. A movie light is clearly visible reflecting off the cop's helmet as the sun is shining in a different place on the helmet.
During the opening credits postcard montage, one of the cards shows a billboard advertising "Gatorland Zoo, 6 miles away", and the post card heading mentions the billboard was photographed at St. Augustine, Florida. Gatorland Zoo is located in Kissimmee, Florida, which is over 120 miles away from St. Augustine. A few postcards later, another card appears from Gatorland Zoo, depicting the "alligator mouth" entrance, and that card is correctly headlined as Kissimmee, Florida.
During the St. Louis part, they show the Griswolds crossing the bridge into Missouri and *then* getting lost in what they title "East St. Louis." East St. Louis is actually in Illinois, so they would have encountered it before crossing the bridge. This has apparently been corrected in the video version.
When Clark first stops for gas and rips the license plate cover off trying to find the gas tank, this is at the Little America hotel in Flagstaff, Arizona, where some other scenes were filmed in the movie. This is a truck stop/ hotel, and the garage in the background is very distinctive, as are the ponderosa pines across the street. This is somehow set between Chicago and East St Louis, while Flagstaff is in the middle of the world's largest ponderosa pine forest. In the Trivia section, it places this gas station in Los Angeles.
Tall mountains can be barely seen in the distance when the Griswalds arrive at and drive away from Cousin Eddie and Catherine's house & farm. There are no tall mountains in Kansas (the highest elevation is only over 4,000 feet above sea level in Wallace County, two counties to the North of Hamilton County, where the town of Coolidge is). The mountains visible in the background are in fact the Wet Mountains near Pueblo, Colorado, where the farm used to film Eddie's house was located.
They are clearly in Colorado (mountains) and Clark says: "Hey, hey, easy kids. Everybody in the car. Boat leaves in two minutes ... Or perhaps you don't want to see the second largest ball of twine on the face of the earth, which is only four short hours away?" The second largest ball of twine is located in Cawker City, Kansas. The largest ball of twine is located in Darwin, Minn. Both of which are clearly east of Colorado and not west, which is where the Griswolds are headed.
In the postcards opening, just after Christie Brinkley's name fades offscreen, the postcard for the "Mystery Spot" lists its location as "St. Ignance, Michigan." The Mystery Spot is located in St. Ignace, not St. Ignance.
When they stop for lunch, the rest area is just east of South Fork, CO. They leave and drive west over Wolf Creek Pass then down towards Pagosa Springs. You can see The Inn at the Pass at the bottom. But they spend the night in tents in South Fork. Did they get turned around at the pass?
When the Grizwolds are "lost" in St. Louis, the wide overhead shot clearly shows the Family Truckster exiting onto Interstate 70 West. This is the correct route for their trip, and they wouldn't have been lost if they took it.
When purchasing a car in Illinois, either your license plates are transferred from your old car, or you are issued a License Applied For sticker to be posted in the window of your car (at that time). The Griswold's old car is driven off and crushed without removing the plates, and there is no sticker on the new car. They would be stopped and ticketed by the first cop that spotted them.
When Clark and the girl (Christie Brinkley) go skinny-dipping in the motel swimming
pool, we hear her voice laughing and shouting, while on-screen, Ellen is swimming underwater and could not possibly have done either.
In the scene in Kansas when Rusty is asking his cousin Dale whether he had "Pac Man", Dale says "no", but in the very next scene in Dale's room, a portable Pac Man game can be clearly seen on the bed behind Rusty. However, this is Rusty'S Pac Man game. He brought it along on the trip and it can be seen in the Truckster many times throughout the film. So Dale saying he does not have a Pac Man game is correct.
When Clark and Ellen are doing the dishes, you can see Ellen just brush the leftover food into the sink and then hand the plate to Clark. She does not wash the dish. Clark is in front of an open dishwasher but he just wipes the dirty dishes with a towel and puts them in the cabinet. This type of subtle joke is a hallmark of Chevy Chase, and was done intentionally as a joke.
When Clark falls onto the skeleton when wandering in the desert, a jaw spring can be seen in the back of the skull. This is used in the lab to keep the jaw shut, but obviously wouldn't be on a skull in the middle of nowhere.
Towards the end of the film, when the Griswald's reach Wally World, Clark tells Laskey that they have an appointment. When the shot switches to Laskey it's clear that he's "reading" off a blank legal note pad.
At the end of the movie there are 2 security guards. One stays behind at the front entrance and the other is taken with the family on all the rides. There is no one left to operate the rides, yet the rides seem to start all on their own.
When the family is riding the Buccaneer, you can see the ride operator. They are supposed to be at the park with only the Guards there. Obviously, someone has to operate the rides, but if the park is supposed to be closed, then the employees are not supposed to be there.