Revealing mistake: When Harry trips on the fan string throwing feathers all over him, the fan sound is heard running but there's no air blowing at him as the feathers are falling around him undisturbed. A few shots later, we see the fan on and blowing feathers around the room which is what it should have been doing.
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 Marley enters the store, his right boot swaps from soaking wet to dry between shots.
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.
Revealing mistake: When Kevin rides the rig on the rope to get to the treehouse, you can see that it was a stuntman who is much taller than Kevin and looks nothing like him.
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.
Character mistake: When Kevin is shooting the toys off the laundry chute with Buzz's BB gun, he's looking through the scope with his closed eye.
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: 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.
Revealing mistake: When Kevin screams from putting on aftershave, the shot cuts to the spider running behind the toilet. You can see white tiny pellets being thrown at the spider from behind. This must have been to make sure it kept moving during the shot.
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".
Other mistake: Toward the end of the film, there is a scene where Macaulay Culkin rides a rig on a rope from his house to the treehouse. Joe Pesci and Daniel Stern try to follow, but Culkin cuts the rope with a hedge cutter. Problem is: The rope is slack when Mac cuts it. With the weight of two grown men, it would have been stressed like a guitar string.
Other mistake: When Harry and Marv are making their way across the rope to the tree-house, you can see them dangling in a long shot. It has to be stuntmen because, despite the 12 inch height difference between the characters, they seem to be the same size while hanging there.
Factual error: Kate flies American Airlines to Scranton, but that airline did not serve Scranton in 1990. Also, a DC-10 is too big to be serviced at Scranton.
Suggested correction: Air Force One, which is quite a bit larger than a DC-10, has landed at Scranton in the past (https://wnep.com/2013/08/22/air-force-one-lands-in-scranton/). Just because DC-10s don't generally land there doesn't mean they can't.
They are much more likely to make an exception for Air Force One than the are for a single family unless it was for something wrong with the flight or an emergency on the flight, not for a connecting flight to Chicago or a chance at a connecting flight.
The idea is that DC-10s can land there for whatever reason.
Kate landed at Dallas first, then flew to Scranton. This is revealed in Kate's rant at the ticket agent.
Air Force One would park at GA parking, not at the terminal. The DC-10 that lands would have very likely parked at a gate for only 737s and smaller.
Revealing mistake: When Kevin lands in the treehouse, he's at the back with his feet through the wall. Given where the rope is tied to the tree, he would have hit into the tree or the door frame of the treehouse, not at the back wall.
Continuity mistake: The Murphy's basement is shown to be dripping water from when Marv flooded the kitchen earlier but when the crooks are hit by the old man at the end of the film, the floor is dry even though the faucets are still running.
