Revealing mistake: In the scene at the end when Marv and Harry are talking to Kevin on the roof, if you watch it when Kevin throws the brick down at them, the one brick hits Marv. They cut film somehow so you wouldn't notice easily, but when it hits Marv you can see the corner buckle in, as it's a sponge made to look like a brick.
Continuity mistake: At the end, Harry walks to the building's door, thinking he can get in. The bag with tools opens and tools fall all over him. After a few scenes, he gets up and you can see that the tools are in one place and not scattered anymore. Plus the bag and string have disappeared.
Continuity mistake: When Kevin is checking into the hotel you can see a pair of legs in the top right hand side of the screen. At one point they walk away and then are back in the very next shot to continue standing while Kevin talks to the hotel lady.
Factual error: When Harry and Marv arrive for the first time at Kevin's "funhouse", they look up to the roof and spot Kevin taking a Polaroid of them. The flash brightly illuminates them both, but the building looks to be at least 30 feet high; a basic Polaroid camera does not have a flash strong enough to reach such a distance (plus the street is already illuminated by lamps and Christmas lights). (01:23:05)DEvans
Other mistake: When the family arrives in Miami, they pass Kevin's bag until they reach an old man, dressed in shorts. In the initial airport scene, while Kevin is chasing his father, the same old man is there, dressed in a business suit.
Continuity mistake: When Harry goes up the steps leading to the back door of Kevin's uncle's house, the wooden planks he kicks away are in a different position to when he first enters the alley.
Revealing mistake: In the whole scene where Harry's head is caught on fire to the part where it shows the explosion outside the building, this is quite obvious that the whole scene was done during the day.
Continuity mistake: Kevin asks the limousine driver, "Do you know any good toy stores?" His glass of Coke is almost empty. When the driver says, "Yes sir.", it is three-quarters full.
Continuity mistake: When the vans from the airport arrive, notice the second van to arrive smashes the statue in front of the McCallister's door all over the pavement. When the whole family is running out of the house into the vans, the statue is standing perfectly again like it hadn't been touched at all, but pieces of the feet were broken off, so it couldn't have just been stood up again.
Continuity mistake: When Kevin is running from Harry and Marv he breaks a fake pearl necklace to spread the beads all over. You can see after he drops them all that they have spread far apart. In the next shot where Harry and Marv's feet are shown there are a lot more beads all together which is why they slipped on them.robsuttonjr
Continuity mistake: The hotel staff and security come up to Kevin's room - Kevin starts playing the tape and fast forwarding and muting when the woman in the scene talks. At the end of the scene when the man in the movie says "maybe I'm off my hinges but I forgive you" the woman lets out a sigh of relief. Kevin leaves as he plays this scene, and the sigh in the movie couldn't be heard.
Continuity mistake: Kevin's mom goes to the 3rd floor to lecture Kevin. When Kevin stands they move shots between mom and Kevin who is standing still. There are 3 separate shots of Kevin in this sequence. In the 1st & 3rd shot his left collar button is covered and his hair bang is above left eyebrow. In the second shot the left collar button is visible & the hair bang is lower touching the left eyebrow.robsuttonjr
Plot hole: The sheer distances Kevin covers on foot in one night are outrageous. Between 9pm and midnight he walks from Carnegie Hall to the children's hospital, to 95th street, back to the toy store carrying a large paint can and a large 2x4 (street signs here put it around 59th and 5th), back up to 95th, then all the way back to midtown, to Rockefeller Plaza. One way from W 95th street to around E 59th and 5th Ave. is at least an hour on foot for an adult, he does this 4 times between 9pm and midnight, once while carrying a 2x4 and paint can, once while being chased by 2 adults, and he still has time to set up a house full of traps.
Revealing mistake: In the scene where Kevin runs into his relative's abandoned house in the middle of the night to set the traps, he runs down a ramp. You can tell that shot was filmed in broad daylight.
Continuity mistake: Before Harry jumps for the ladder, there are several close-ups and there is nothing on the bottom rung. When Harry jumps, the bottom rung is suddenly covered in green goo causing him to slip.