Revealing: When Marion is driving her car through the night, she keeps looking at her speedometer. You can clearly see that the gear shift lever is in "park" as she is driving.

Deliberate "mistake": When Norman picks up Marion's body to carry it to his trunk, a bra is visible through the shower curtain. Gus Van Sant included this goof in his 1998 remake.

Visible crew/equipment: While Janet Leigh is being stabbed to death by Mother, as Janet turns around in the shower, it is possible to see part of the moleskin that Janet wore for the scene for a split second.

Factual error: When Janet Leigh is shown lying dead on the floor of the shower, there is a close-up of her open eye. The pupil is contracted to a pinpoint (obviously due to the bright lighting) where it should have been dilated. After the film was released, Hitchcock heard from several ophthalmologists who pointed this out and suggested he use belladonna eyedrops in the eyes of "dead" people in future films, as the chemical prevents the pupils from contracting.

Factual error: At the end of the film in the Sheriff's office, you can see a wall calendar with the date on 17. The film started on December 11th - Marion absconds with the money on the same day. She slept the first night in her car, then drove all day Saturday before arriving later that night at Bates motel, she was killed the same night. When Arbogast arrives we learn that Marion has been missing for one week, it is now Saturday, Sam and Lila visit the motel to look for Arbogast, (who by now is dead) and they go to visit Sheriff Chambers later that same evening. They meet the Sheriff the following Sunday morning outside the church, it is on the same day that Norman is captured and taken into custody, now the date on the wall calendar should have shown 20 and not 17, the story has lasted for a total of nine days and not six days.

Continuity: When Marion and Norman are talking after he has brought in some sandwiches, Marion tears the same piece of bread 3 times on different occasions.