Visible crew/equipment: When Kevin is in the house and he locks the front door, a crew member is reflected on the mail holder.
Revealing mistake: When Marv is trying to break into the basement, after he slides down the stairs and is trying to use the crowbar to hoist himself back up, the "ice" on the floor looks "too perfect" and is either a greased up glass sheet or plastic (to allow him to slide his feet around comically). You'd sort of expect the ice to be a bit uneven naturally. It's more evident in HD or digital versions.
Continuity mistake: When Marley comes into the drug store to see Kevin, the wrapping paper is leaning on the shelves, but in the next shot the wrapping paper is gone.
Continuity mistake: When Kevin puts the spider on Marv's nose you can see a box of junk is almost halfway off the steps of the attic but in the next shot at the start of the film the box is no longer halfway off the steps.
Continuity mistake: When Kevin is washing dishes, there's Bubbles on his hands, but in the next shot there's no bubbles on his hands.
Continuity mistake: Harry and Marv both get hit with the paint containers on the stairs. Look at the front doorway when Marv gets hit. The cord (from the hot implement attached on the doorknob) is in an 'S' shape and lots of micro machines litter the doorway. Harry then gets hit. When he gets up to go up the stairs after Kevin, the cord has moved and the micro machines are well clear of the doorway.
Continuity mistake: When the 2 burglars are breaking into the McAllister home, the tall burglar gets hit square in the face by an iron...he has iron marks on his forehead and cheeks but not his nose...how could the iron not hit his nose?
Factual error: Plane doors are only closed when the flight is ready to take off and most passengers have been accounted for. They are not reopened for late passengers, so in reality the family would have been left behind.
Other mistake: When Gus Polinski talks about his music, he mispronounces "Daj mi buzi" (Die-Me-Boo-Gee) as "Domavougi." "Daj mi buzi" is Polish for "Give Me a Kiss."
Suggested correction: I think this is meant to be a "deliberate mistake ", which didn't show up as an option to suggest making the change elsewhere (under "edit"). It appears to be part of the comedy - he should know how to pronounce it. Another opinion would be helpful.
Revealing mistake: When old man Marley hits Harry and Marv with the shovel at the end, you can see it's actually a stunt man doing the hitting motions.
Revealing mistake: When Harry tells Marv to go back while they are climbing across the rope, in the shot facing them front-on, you can see Kevin in the background about to cut the rope. If you look closely this is not Kevin, it is his stand-in.
Continuity mistake: In the supermarket when Kevin puts the groceries on the conveyor belt, he sets the tissue paper standing up. The next shot of Kevin shows the tissue on its side and farther back, the next shot it's back to its original position.
Continuity mistake: Right before Kevin destroys the shelves after climbing up to reach the metal box, the box with Buzz's life savings (on top of the shelves in his room) moves between the overhead and ground shots.
Continuity mistake: Kevin's hands change during the micro-machines sequence. He is sitting at the top of the steps, and puts his right hand down. In the next closer shot, both hands are in a different position.
Continuity mistake: After Kevin's whole family comes home, he walks straight to the window to look out. If he had done that, he would be looking out of the side of the house, but he is obviously looking out the front of the house to straight across the street.
Continuity mistake: When the delivery guy stands outside the door and Kevin plays the movie, in the shot from Kevin you see the red curtains are more wide open and you see the silhouette from the delivery guy. In the shot from the delivery guy the red curtains are suddenly more closed and his silhouette couldn't be showing through.
Continuity mistake: When Kevin puts the groceries on the belt, there's 2 packs of toilet paper. One in the front and one in the back behind the orange juice. When she scans the orange juice, the other pack of toilet paper isn't there.
Continuity mistake: When Kevin climbs on the shelves in his brother's bedroom you can see the spider switch to left and right.