Continuity mistake: When Marion arrives at the Bates motel, she sounds the car horn for the first time, the windscreen wipers are switched on. She gets out of the car, looks towards the old house, then goes back to the car, as she sounds the horn for the second time the windscreen wipers are now switched off.
Visible crew/equipment: When Marion arrives at the car dealership, the salesman sees her and starts walking towards her. If you look carefully, there is a wire trailing out his trouser leg, most likely for a hidden mic.
Revealing mistake: After Marion's sister and boyfriend look through the Number 1 bathroom and find the ring on the toilet, they turn off the light. On the wall behind them you can make out a square beam of light, but no other lights are on in the cabin.
Revealing mistake: When Marion's boyfriend and sister visit the Sheriff and his wife at home, there is a camera shot where you can see that the living room background scenery ends and there is no ceiling.
Other mistake: In the shower scene, Marion Crane's palm looks water wrinkled as if she's been in the shower for quite a long time even though she was only in for a few moments before Norman stabs her. Also, when Norman drags her out of the bathroom, Marion's legs are stiff and together and she has her toes pointed.
Continuity mistake: When Mother Bates leaves the motel room after stabbing Marion, she leaves the room door wide open. When Norman reaches the door to check on Marion, the door is closed.
Continuity mistake: Norman brings a tray of food to Marion, when she says "So long as you've fixed supper we may as well eat it," watch how her folded arms change position from hands tucked underneath, to hands on top of her arms.
Continuity mistake: When Marion is buying another car at the dealership, in the background you can see the same extras walking in different directions on the sidewalk.
Visible crew/equipment: When Marion arrives at the car dealership and the salesman says "be with you in a second", pay attention to Marion's car door. You can see the reflection of a crew member kneeling down as soon as she starts walking away from the car.
Deliberate mistake: Mrs. Bates is in a rocking chair, but in the close-up that reveals her face her position smoothly rotates as though she were in a swivel chair.
Continuity mistake: When Norman carries Marion's dead body out to the boot of the car, the water on Marion's bonnet changes between shots. In some shots there is water, sometimes there is no water.
Continuity mistake: When Norman is parking Marion's car, he does so by reversing with right hand lock. But when he drives off, he does so with left hand lock without having turned the steering wheel.
Deliberate mistake: After being stabbed, Arbogast falls down the stairs in an impossible manner. He is standing tilted backwards all the way down the stairs.
Plot hole: When the cop comes back after making the phone call, he's just missed Norman. He heads over to the office and calls out for Bates. He's in there around 45 seconds. Then he leaves and heads towards the big house. How can Norman be at the house ready to kill him in his mothers clothes, when he had no idea the cop was back and he would not have had time to get there from where he was, right at the far end of the cabins?
Suggested correction: Because Norman heard/saw him coming up the road. Norman hesitates before he goes into a cabin or behind one, it's not clear which. He has seen Arbogast's car before and recognizes it. He goes the back way between the two buildings of cabins (just like Vera miles does later when she goes to the house) and up to the house to put the dress/wig on and be ready for Arbogast when he gets to the top of the stairs.
Continuity mistake: When Arbogast reaches the top of the stairs, Mother Bates stabs him in the chest; but when the camera angle changes, the wound is on his face.
Suggested correction: That's blood splatter, not the wound.
Audio problem: When Norman enters the cellar to kill Lila and is grabbed from behind by Sam, Mother's voice can be heard yelling, "I am Norma Bates." However, this was added in post-production, as his lips are not moving.
Continuity mistake: The shadows made by the sunlight streaming onto the hotel office wall completely change, from the scene in which Sam grills Norman about the $40K, to the shot in which Norman runs out to find Lila. While Sam and Norman were in the hotel parlor and Lila was in the house, who pulled the office window shade half way down - Mother?
Other mistake: If the film begins on Friday, December 11th and continues to the following week, there should be more Christmas decorations, not just the ones seen on the store when Mr. Lowry walks by Marion's car.
