Trivia: When Kevin is in Buzz's bedroom, he finds in the box a picture of Buzz's girlfriend. This is actually a picture of the art director's son dressed up to look like a girl, because the director, Chris Columbus, thought it would be too harsh to make fun of a girl like that.
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 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: 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: In the scene where Kevin is shooting the BB gun at action figures he has lined up along the laundry chute the baseball player figure he sets up is leaning against the left hand side of the laundry chute frame, yet when he begins to shoot at the figures the baseball player is standing up straight on its own and not leaning against the chute frame any longer.
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 putting washing in and taking clothes out of the dryer, he places the orange bottle of liquid on top of the washer with the handle facing away. On taking the clothes out of the drier and closing the door, he turns to see the metal heater scaring him by saying "Kevin." Look over his left shoulder when the shot comes back to Kevin, the orange bottle now has it's handle facing outwards, and the top isn't on properly.
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: 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: 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: 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 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 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.
