Continuity mistake: Buzz comes down the stairs 3 seconds before Kevin, but manages to eat Kevin's entire cheese pizza in the next shot before Kevin could enter the kitchen. (00:08:04 - 00:09:20)
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: When Frank squishes Fuller with the chair, we see Frank walk off. However about 5 seconds later we see Frank's wife rescue Fuller, and Frank walks off again. (00:09:35)
Suggested correction: Not a mistake. Frank never walks off the first time.
Perhaps the wrong phrase was used. He actually moves away from the front part of the seat to the left and out of shot of the camera. When the shot is shown of Frank's wife rescuing fuller, Frank repeats his actions of walking away from the front part of the seat and moving to his left. There is no reasonable reason he would move back in front of the chair for the purpose of repeating this action. Especially since his wife is trying to rescue Fuller and would not permit Frank to return to his original position. So the mistake is valid, just an error in wording.
Continuity mistake: When Kevin goes outside the first time and sees the cars in the garage, the light isn't on. When it shows the garage again in the next shot, the light is on. (00:20:25)
Suggested correction: The light could be motion activated. Either Kevin's movement or passing vehicles could have turned it on, regardless of the time of day. I have motion detector lights in my carport and they constantly go on and off in the daytime if it's low-light and cars pass by fast enough. People walking their dogs can also activate it if they are close enough. They sometimes stay on until I have to manually turn the power off, then on again.
That would explain it only if the light came on when Kevin "activated" it. It stays off during the first scene, and he doesn't make any motion towards the garage when the camera is on him. Nor do we see any vehicles or people pass behind him.
How likely is it that this movie - taken in 1990 - had access to the developed technology that we have today, to make automatic lights turn on?
Infrared motion sensors were around in the 80s.
Continuity mistake: When Kevin is searching in Buzz' chest, some objects appear or change place after he throws the Playboy magazine away. (00:21:45)
Continuity mistake: In the scene where Kevin prepares to ride his toboggan down the stairs, the front door changes position between shots from half open to completely open. (00:25:20)
Continuity mistake: When Kevin goes to the grocery, he buys Tide detergent. While walking home, the two bags break, but no Tide detergent falls out.
Continuity mistake: When Marley enters the store, his right boot swaps from soaking wet to dry between shots.
Continuity mistake: When Kevin is leaving the church after talking to the old man that lives next door to him, he runs home. Between leaving the church and getting home he is wearing one pair of trousers, when he gets home he is wearing a pair of jeans, then when he is setting up the traps for the bad guys he is back to the first pair.
Continuity mistake: When Joe Pesci places his hand on the red hot doorknob on the front door of Kevin's house, he places his hand on the doorknob sideways, but after he sticks his hand in the snow, he looks at his hand and the letter M that was burned into his hand is straight up and down, not sideways like it should be based on how he grabbed the doorknob.
Continuity mistake: When Kevin is shooting the BB gun at action figures he has lined up along the laundry chute, there is a baseball player figurine leaning against the side of the laundry chute. A few shots later, when Kevin begins shooting at the figurines, the baseball player figurine is no longer leaning against the laundry chute frame, instead standing unassisted.
Continuity mistake: When Kevin is putting washing in and taking clothes out of the dryer, he places a bottle of Tide detergent on top of the washing machine with the handle facing away from the camera. Upon taking the clothes out of the drier and closing the door, he turns to see the furnace scaring him by saying "Kevin." When the camera faces Kevin again, the bottle of detergent is turned so that the handle faces the camera, and the cap is no longer fastened correctly.
Continuity mistake: Kevin goes out to cut the top off a tree to use as a Christmas tree. The tree top he drags in is much smaller than the one he decorates.
Continuity mistake: Kevin sits down with a meal before the Wet Bandits arrive at the house consisting of macaroni and cheese on a plate. When Harry eventually makes it to the dining room, he is pelted with feathers. Look at the table to the left. A three part microwave meal still in its white plastic container now sits on the plate.
Continuity mistake: When Marv comes to the back door while Kevin is washing dishes, Kevin turns on the Johnny & Snakes movie. Then he goes to get the pot and puts the pot by the back door. The whole time he has his sleeves rolled up, but when he opens a drawer to get firecrackers, his sleeves are rolled down. In the very next shot they're rolled up again. The shot changes too quickly for him to roll them back up.
Continuity mistake: In the scene where Kevin is hanging up ornaments on the Christmas tree and he sees Harry peeping through the window by the reflection of the ornament, the reflection is not entirely accurate. It shows Kevin facing the camera with both the tree and window behind him. The reflection should have shown Kevin with just the window behind him and slightly to his right, based on his original position.
Continuity mistake: When Kevin says, "I made my family disappear" and runs around the house, he runs to the foyer and spins in a circle. The window near the stairs is dark meaning it's dark outside. He run upstairs and the window in Kevin's parent's room is also dark. The lights are on too. He then goes to Buzz's room and the kitchen and it's light outside. No lights are on.
Continuity mistake: Right after Marv loses his shoes on the tar covered stairs he goes back outside to go in the window. When he's running in the snow you can see that he is wearing little pink booties so his feet don't get cold. When he is getting into the police car at the end, you see a short shot of his feet when he's almost in and you can clearly see he has black boots back on.
Continuity mistake: The plane for Paris leaves in the morning - around 10 am. Shortly after take-off (it is still morning in Chicago) it is dark outside the windows. Even though the flight path from Chicago to Paris goes a bit north, it would not get dark that fast.
Continuity mistake: When Kevin plays the video when the guy comes to deliver the pizza, the guy on the video says "Hey. I'm gonna give you to the count of ten." When Kevin first saw the movie, the word "Hey" was never spoken. The line immediately before "I'm gonna give you to the count of ten" was "I'll tell you what I'm gonna give you, Snakes".
