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?
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: 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: 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)