Home Alone (1990)

Continuity mistake: When the robber with the beard gets hit in the face with an iron, the iron hits him on the face, and leaves a mark slanted to the right. It also leaves a mark on his nose. When the two robbers are talking after they have been tricked and before Kevin puts the spider on one of the robbers, the iron mark is vertical and there is no mark on the nose anymore.

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.

Sacha

Revealing mistake: In the scene where Kevin goes to climb the shelves, we can see that the tarantula is fake as it doesn't move, nor would its legs be spread out if it was holding onto the side of the glass tank as shown.

Factual error: In the scene where Kevin swipes the toothbrush from the drugstore, he slides across a skating rink on his knees while being chased by the cop. Ice is slippery, but not THAT slippery (especially when it's been skated on). Kevin would have only slid a few feet before coming to a stop.

Visible crew/equipment: When Kevin is decorating the Christmas tree you can see a crew-member reflected in the Christmas bauble.

Visible crew/equipment: When Kevin is going to swing over by the tree house on a rope, before he goes you can see a crew member reflected on the wall by the window.

Revealing mistake: In the scene where John Candy and Catherine O'Hara are in the van and John Candy plays the clarinet, he never changes the positions of his fingers, but he plays a different note.

Visible crew/equipment: When Kevin's sleigh flies through the entrance door, the person riding it is an obvious stunt: Bulkier and way bigger than Kevin.

Sacha

Continuity mistake: When Kevin is dancing to 'Rocking Around the Christmas Tree' in the living room, the position of the record player is straight, but in the next shot it is halfway crooked.

Continuity mistake: When Kevin is shopping for groceries the paper towels are in the cart, but in the next shot the paper towels are on the conveyor belt.

Visible crew/equipment: When Kevin is getting ready to light the firecrackers you can see a crew member's face reflected on the dishwasher.

Visible crew/equipment: When Marv is in the basement he closes the door behind him while he is getting ready to be hit by the iron you can see a crew member reflected on the basement door.

Continuity mistake: When Mrs MacAllister is trying to get on the plane to Dallas, it is light in Paris. The movie cuts to evening scenes in Chicago. That cannot be. If it is evening in Chicago it is either night or very early morning in Paris - too early for it to be light. And when the plane takes off, it is darker than during check-in - showing that it is evening and not morning. December dusk in Paris is noon in Chicago.

Continuity mistake: When Harry slips and somersaults down the Mccallister's iced front door steps for the second time, his hat falls off at the base of the stairs while he's tumbling, yet in the subsequent shot showing Harry, he is wearing his hat again.

Continuity mistake: Marv is walking up steps full of goo in the basement. He gets some goo on his feet and we see it in the nail scene. When he falls and grabs his feet, his feet are clean from then on.

manthabeat

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: 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.