Visible crew/equipment: When the pizza guy arrives at the start, as he gets out of his car a stage light is reflected in the paintwork. This cannot be the street light as that is a more yellow and dull reflection, further along the car. (00:06:50)
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)
Revealing mistake: When Kevin's cousin Fuller is trapped behind the kitchen chair during the spilled soda incident, the "wooden" chair back which hits him in the nose actually bends when it hits his face. (00:09:25)
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.
Revealing mistake: The morning the McCallisters are rushing to get to the airport, the kid from across the street is bothering one of the van drivers. In the scene where the van driver says, "Gee, kid I dunno, hit the road," you can clearly see the kid mouthing the words as the man speaks. (00:14:00)
Visible crew/equipment: When Kevin first realises he's home alone and goes into Buzz's room, there is the leg of a crew member to the bottom right of the picture (wearing jeans). (00:19:20)
Suggested correction: Not visible at all.
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)
Audio problem: When Kevin is going through Buzz's private things he finds a picture of his girlfriend. Sickened by her appearance, he smashes the picture. But the smashing sound starts before he hits it. (00:22:05)
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)
Other mistake: Kevin rides down the stairs on his sled and out the door. He originally lined up the sled at the top of the stairs, but it is clear that the stairs lie to the right of the door. His sled went straight down the stairs, therefore making it impossible to go straight out the door in one movement as shown. (00:25:25)
Revealing mistake: As Kevin is flying off the front porch on the toboggan, you can see the small wheels mounted on the bottom of the sled to aid in its "jump". (00:25:30)
Revealing mistake: When Harry walks around the side of the house towards the front door, in the shot which shows Harry walking from side-on, this is obviously a stand-in, given this person is much taller than Joe Pesci (who plays Harry). It is also the same stand-in when we see Harry in the behind shots as he holds onto the railings while he tries to climb the steps. (01:14:10)
Revealing mistake: Towards the end when Harry walks up the frozen stairs, you can see it switches to a stuntman when he slips and lands on his back. (01:17:55)
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. (01:22:30)
Revealing mistake: Whenever Marv is outside walking in the snow in his bare feet you can tell that the feet aren't real. (01:22:30)
Revealing mistake: When Marv is about to hit Harry, who has the spider on his stomach, you can tell that, for two shots, it's a fake spider. The real spider is brown. In the shots where Marv is standing about to hit it, the spider is black and motionless. (01:26:00)
Revealing mistake: When Mr. Marley clobbers Marv (Daniel Stern) with the snow shovel, Daniel Stern's stunt double is seen.
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.
