Dumb and Dumber (1994) - 7 major mistakes

Continuity: At the beginning of the movie, Harry's van has bucket seats, yet later on when the "gas-man" rides along, he is sitting on a bench seat in-between Harry and Lloyd.

Continuity: When Lloyd tackles Mary on the hotel stairs, she is wearing black pantyhose. By the time they get to the hotel room, she has miraculously changed into grey tights.

Continuity: When Lloyd asks if the bartender knows Mary, he originally grabs the bartender with the left hand.  But in the next shot he lets go of him with his right hand.

Visible crew/equipment: When Lloyd is daydreaming about Mary as the doors to Mary's house open and Lloyd picks up Mary. He lifts up her skirt to show a little flesh, in the background you can see the feet of two crew members laying on the ground holding the doors open.

Audio problem: When Harry and Lloyd pick up the hitchhiking natives, when they were playing the mockingbird song, the guitar was playing but his hands weren't moving at all.

Continuity: When Lloyd drops Mary off at the airport and hugs her goodbye, in the background there are two men walking towards them. The camera changes to the angle behind Mary then behind Lloyd and then back to the side. When it returns to the side view the two men are farther away but still walking toward them.

Continuity: When Harry and Mary go out on the date to the ski resort, when they get into a snowball fight, the camera shows Harry, and it's snowing, but when they show Mary (who is supposed to be right beside him) it is not snowing. It keeps doing that, when it shows Harry it's snowing, and Mary it is not (or vice versa).