Continuity mistake: In the scene where Kevin goes flying into his treehouse and breaks out the wood, the amount of wood missing changes from one scene to the next.
Continuity mistake: When Kevin is preening himself in the mirror while giving a running commentary of his washing habits, you can see the shower gel (facing forward), aftershave and deodorant to his left by the sink. When it cuts to a close shot, a bottle of fragrance has mysteriously appeared by these items and the shower gel is facing away from Kevin.
Continuity mistake: In the scene where Harry tells Marv to go down to the basement door, Marv slips on the icy stairs and falls down to the bottom of the stairwell. At the bottom of the stairs from the camera shot from above you can see an accumulation of snow on the stairs and in the bottom stair well. Yet when Marv finally opens the door and enters the basement all the snow that had accumulated in the stair well has now disappeared.
Continuity mistake: When Kevin's mom is in Scranton at the airport counter, her coat is resting on her shoulders so that it's open. In the next shot, the coat is closed more, so the sides are close together.
Continuity mistake: In the shot where Buzz is eating the slice of pizza, he is shoving it into his mouth all bent up. In the next shot from another angle, he is eating it flat and it seems to be a whole new slice. (00:08:50)
Continuity mistake: In the scene where the robber is breaking into the basement, the steps and concrete by the door are icy. However, when the camera angle changes and it shows the same scene looking out of the basement, there is no ice at all.
Continuity mistake: When Harry is telling Marv when the Christmas lights on the house are going off, right before they are going to rob the house, they show the dashboard of the van. There is nothing on it. When they pull into the driveway, there's paper and other things on the dashboard.
Continuity mistake: When Harry and Marv are first stalking Kevin in their van, they pull up to the curb and stop at an angle to it. In the next shot, the view out the back of the van and the view of the van from the front show the van parked parallel to the curb.
Continuity mistake: When Kevin is hiding in the nativity set, you can see him on the right, just covered in the green robe. When it changes to the close up shot, he's now holding a shepherd's staff, which would have been visible in the previous shot.
Suggested correction: There is a staff but it's hard to see. If you squint a little, you will see it.
Then you're seeing something else because it would be easy to spot and there's nothing there.
Kevin is definitely holding the staff in all shots, you can see the curved head of the staff against the background.
Continuity mistake: As Kevin runs away from the nativity scene after hiding from the Harry and Marv, his scarf is done up to the right (over his right shoulder). When he reveals himself from the nativity scene from under the green robe, his scarf is done up to the left (over his left shoulder).
Continuity mistake: The iron that hits Marvin strikes his forehead, but after, the imprint is across his whole face.
Continuity mistake: When the robber with the beard gets hit in the face with an iron, the iron hits him on the face, and leaves a mark slanted to the right. It also leaves a mark on his nose. When the two robbers are talking after they have been tricked and before Kevin puts the spider on one of the robbers, the iron mark is vertical and there is no mark on the nose anymore.
Continuity mistake: When Kevin puts down his milk and snack on the table, he is looking at the presents under the tree. When he wakes up thinking his mom might be home and calling for her, when he goes in the room where the tree is, there are no presents.
Continuity mistake: When Marv and Harry first attempt to break into the McCallister's house, Harry tells Marv to go to the basement, and he goes to the front door. With the front steps covered in ice, Harry slips and falls down the steps, and his crowbar clanks down at the bottom of the first step. When Harry gets up and continues trying to get up the steps and into the house, the crowbar disappears - it is not in his hands.
Continuity mistake: When Kevin is shooting toys off the laundry chute, his rifle is cocked by pushing forward on the slide, then pulling back. Later, when Kevin is shooting Marvin in the pet door, Kevin pulls back on the slide, then forwards to cock the gun.
Continuity mistake: When Marv slips while walking down to the basement, he lands on the right side of the steps. When the angle changes, he is laying on the left side.
Continuity mistake: When Kevin is dancing to 'Rocking Around the Christmas Tree' in the living room, the position of the record player is straight, but in the next shot it is halfway crooked.
Continuity mistake: When Kevin is shopping for groceries the paper towels are in the cart, but in the next shot the paper towels are on the conveyor belt.
Continuity mistake: When Kevin puts the food in the casher you can see a lot of people next to him, but in the next shot there's only one person behind him.
Continuity mistake: When Harry slips and somersaults down the Mccallister's iced front door steps for the second time, his hat falls off at the base of the stairs while he's tumbling, yet in the subsequent shot showing Harry, he is wearing his hat again.
