In the scene where Roman and the girls are sitting in the boat, Katie is wearing a halter but when the boat takes off she is wearing a jacket. In the next shot of the boat she is wearing just the halter again.
When Bart the Bear was trying to attack Roman on the staircase, you see the bookcase and its books knocked over and scattered all over on the floor below, but in the next scene it's cleaned up.
The lampshade on the lamp-gun that Chet shoots the bear with, near the end of the movie, suddenly disappears right before it is shot.
When the car is parking inside the four trees at the start of the film the right rear side of the car is an inch or two away from hitting the tree, but when the doors open the tree is a foot or two away.
When Roman is driving back to the cabin to make amends with Chet, it is a torrential downpour. But the reflection in the windshield of the car reveals blue skies with some scattered clouds.
Roman tells Chet that when he lost everything, he had to surrender his seat on 'the exchange', and that he now wears a blue runner's jacket at work, and fetches coffee. Regardless of which exchange he is referring to (CME or CBOT), runners' jackets are 'gold' (Orange), not blue.
The movie supposedly takes place in either Wisconsin or part of Canada close to the U.S. Midwest which would be Ontario. Grizzly Bears such as the "bald-headed" bear that attacks the cabin towards the end are not found anywhere near those areas.
Alcohol burns blue. It would take an enormous amount of flammable substance to produce the fireball that escapes the chimney.
When Roman picks the meat off the grill with his bare hand, this is unrealistic as the meat would be too hot to handle.
The Boat has a Supercharger on it, but when he starts the boat the supercharger belt doesn't spin! In every scene it doesn't spin.. therefore it is not a real supercharger and just for show!.
When Roman tells Chet about overhearing his insult in the men's room at his wedding Roman states that Chet was talking to his father-in-law. But when Roman comes back to make amends with Chet he tells him that he'd made up the story about Chet and his brother, not his father-in-law, in the john at the wedding.
While this would appear to be an error, Roman admits he made the story up - most likely in the heat of the moment - so it's not inconceivable he wouldn't remember specific details of his lie.
While this would appear to be an error, Roman admits he made the story up - most likely in the heat of the moment - so it's not inconceivable he wouldn't remember specific details of his lie.
After Chet finishes the Old 96er and everyone is back at the cabin. Chet runs to the bathroom with everyone chasing him. As the camera pans out, you clearly see Dan Akroyd counting down for everyone to scream and run out of the cabin.
A stick being waved under the bear's chin to make it knock down the cabin door.
When Chet starts to waterski Ben yells out, "Dad, let go of the rope!" Before he says that you can tell by the people in the background that the scene is being sped up.
When Chet and his family open the vehicle doors and hit all of the trees, two of them shake as if they were props.
When they pull up at the bear dump, the girls asleep in the back change positions.
Buck is shown at the carnival in a steady downpour of rain, although neither he nor any of the people are wet.
When Chet is skiing and jumps the bushes, a small ski ramp is visible.
After the restaurant cook personally serves Chet his Old 96er, he remains in the dining area in his bloody apron throughout the meal. Not only would this be a major health code violation, but it also raises the question of who is doing the cook's job that whole time, as the restaurant appears quite busy.
When Roman is about to get in his car at the end of the movie, it is already running, yet when he closes the door, the car is heard starting off-screen.
When Cara and Mara are out in the rain before they go into and slide down the mine shaft, they're heard talking for the first time to one another, but it is clearly overdubbed.
When Chet is explaining water skiing to Ben, one shot shows the boat in the background behind the two while they are talking. Although the boat is heard idling, it clearly is not running in this shot (the blower belt is not turning).
After Chet starts the speedboat and Roman yells "You got it in Neutral!", Chet pushes the throttle forward. When the boat speeds up the ramp, a cord is visible attached to the boat, possibly pulling it up the ramp.
At 10:55 mark, as Chet Ripley gets up from the rocking chair, a camera is briefly visible in front and to the left of him.
Camera shadow clearly visible during the opening credits as everyone sings in the car.
The movie is set in Wisconsin, but several scenes, including the opening scenic drive near the resort, show mountains. There are no mountains in Wisconsin.
Throughout the movie, the characters make reference to being in Wisconsin, but when Chet and the kids go to visit the old man for his 109th birthday, Chet refers to the man as the oldest living person in Canada.
All indications are the movie is set in Wisconsin yet in the opening scenes as the Jeep is driving en route to the cabin, a deer is seen swimming across a lake but it is clearly a mule deer. Wisconsin has Whitetail Deer but no Mule Deer. The closest wild Mule Deer is probably 1,000 miles away.
The bald-headed bear that is referenced throughout the movie is a brown/grizzly bear and not found in Wisconsin.
When Chet is throwing up, Roman (Dan Aykroyd) can be seen giving a cue for the other actors in the scene to run away.
At the very end of the movie with the end credits when everyone is dancing to Land of 1000 Dances, there are shots of Chet happily dancing to the song / having fun and shots of him not happy.