Continuity mistake: When the Lutz's get their first house call, the clothes in the suitcase, on the end of the bed, change between shots. (00:14:20)
Continuity mistake: When George locks the boat house door, you can see inside the boat house through the cracks in the door, but there is no boat visible inside even though there was a boat there in the previous shots. (00:21:10)
Factual error: After George and Kathy leave the Doctor's office they drive through town. When they are talking in the car there is a shot where, next to George's face, you can see the sign of the town hall where the scene was filmed, 'Village of Antioch' in Antioch, Illinois. (00:46:00)
Revealing mistake: Ryan Reynolds is wearing red-eye contacts. You can see the whites of his eyes around the red circle of the contacts in several scenes - most noticeably, right after the home movie he's watching down in the basement melts.
Suggested correction: Not a mistake. Ryan Reynolds actually had bloodshot eyes from being awake for nearly two days of filming. He stated it in an interview for the movie.
Other mistake: Towards the film end, when George climbs up stairs with the gun to kill others, he walks into the passage and shuts the door. A mirror is there in the passage, but there's no reflection of George in it. (01:15:15)
Continuity mistake: After Kathy falls into the water and gets her hair caught in the boat's rotor, she climbs out of the water and onto the deck. Between shots her hair becomes much drier and more stringy, and her face is dry. (01:09:20)
Continuity mistake: When George cooks eggs, the egg spills over the frying pan. In the next shot it doesn't. (00:05:30)
Continuity mistake: When Kathy and George are in the Italian restaurant, between shots George picks his wine glass up twice. (00:30:25)
Visible crew/equipment: When George leaves the room after receiving the phone call from Kathy's mother, a boom mike dips into view, reflected in the large ornate mirror at the head of the bed. (00:14:50)
Continuity mistake: When Harry, the dog, scratches at the wall, a large slab of concrete laying on the floor, by the wall, vanishes. (00:26:05)
Continuity mistake: In the scene where George talks to Billy about the key incident in the car, in the overhead shot the car is speeding very fast. In the next closeup, through the window we can see the car is now going much slower. (00:27:05)
Continuity mistake: When Kathy and George spot Chelsea up on the roof, Kathy races up the stairs, her sweater buttoned up. In the next shot as she enters Chelsea's room, the sweater is wide open and unbuttoned. (00:45:10)
Continuity mistake: Towards the end of the movie after George falls, and the rest of the family is climbing down, we see (from top to bottom of ladder) Kathy, Chelsea and then the eldest kid, with the youngest boy still reaching out on the roof. Yet, in the next shot, the eldest kid and Kathy are on the ground, and Chelsea is on top of the roof again, jumping into Kathy's arms.
Continuity mistake: After Kathy gets her hair caught in the boat's rotor, she runs back to Chelsea, through a downpour. But when George appears, he is dry, despite having to have had to run through the downpour as well. (01:08:40)
Continuity mistake: When George is awakened by the dog barking, George walks down the hall with his shoes tied. In the next shot, as he exits toward the opened door, his shoes are untied. The following shot shows George walking across the deck with his shoes tied once again. (00:54:55 - 00:55:45)
Factual error: There is a poster for Whitesnake on Billy's wall. This movie takes place in 1975. Whitesnake didn't form until three years later.
Factual error: There is an Alice Cooper poster on the wall of the boy's bedroom. The logo on the poster was not used before the 2000's.
Continuity mistake: When George kills the dog in the boat house, he leaves the axe behind. Later when he goes after Kathy, it's back stuck in a block of wood by the house.
Other mistake: The type of pan George uses to make eggs is far more modern a design than when the movie is supposed to take place in the late 70's.
Revealing mistake: Towards the end, when the family is getting away from the house in their boat, you can see that the motor is a covered camera. It is too high out of the water to be a real motor and when the shot is not from behind the boat you can easily see the "motor" moving left and right while the boat is still.
