Continuity mistake: After Norman argues with Mr Toomey, before he goes up to the house, you can plainly see the light on in the living room where Mary is sitting. When Norman goes in the house, Mary is sitting in the dark and Norman then turns on the light.
Visible crew/equipment: When Dr. Raymond leaves with Mary in his car after talking to Norman, when he drives off the entire crew and equipment can be seen reflected in the side of his car. (00:41:50)
Revealing mistake: At the end when Norman is being stabbed at by Mary dressed up as Mother, Mary stabs Norman in the hand. You can plainly tell that this hand is a doll, as it is not a natural colour, it is stiff and is stationary, unlike Norman who is moving his hands. (01:35:10)
Continuity mistake: When Norman is painting the motel, he is distracted by someone looking out the curtains of his house and he drops the paintbrush straight. But in the next shot the paint brush has moved at a forty-five degree angle to how it landed. (00:43:55)
Visible crew/equipment: When Norman accidentally knocks his suitcase down the stairs, when it reaches the end of the stairs a hand can be seen reaching for the suitcase to stop it rolling past the camera's view. (00:10:15)
Continuity mistake: When the two teenagers are down in Norman's fruit cellar, and a "lady" with a knife is chasing the boy, he leaves finger markings on the fogged up window. But by the next shot they have changed. You can tell because when the boy made the markings, his thumb and his index finger markings intersected, but when the camera angle changes the finger prints don't intersect and they are noticeably straightened also. (00:49:45)
Revealing mistake: When Norman hits Mrs. Spool over the head with a shovel, she falls to the ground. In the brief shot of her falling, you can see Mrs. Spool is a dummy. Also later when he carries her up the stairs, she is a dummy. (01:43:25 - 01:44:05)
Revealing mistake: When Toomey is at the motel packing his clothes after Norman fired him, he is startled by "someone" and he turns around and gets slashed with a knife in the face. Before Toomey gets slashed though, you can see a prosthetic scar on his face and a wire in the top right hand corner to trigger the prosthetic scar to open up and look like a knife wound. (00:38:40)
Plot hole: The police let Norman back to his house on the same night multiple murders happened. He is even allowed into the fruit cellar, where most of them happened. (01:38:25)
Visible crew/equipment: When Dr. Raymond comes to visit Norman at the motel, he starts to talk to Norman as he is getting out of his car. As he starts to walk over, a boom mic pole following Dr. Raymond can be seen reflected in the back of his Mercedes for a split second. (00:39:10)
Continuity mistake: Near the end where a lady is coming up the stairs to the Bates house, her hair is tied up much like the "Mother" wig, but when the lady arrives, who turns out to be Mrs. Spool, her hair is parted very differently. (01:40:40 - 01:41:10)
Continuity mistake: When Norman arrives home, he is startled by a note that is found beside the phone and he accidentally knocks his suitcase down the stairs and most of his clothes land on the top of the stairs. But as the camera angle switches to the bottom of the stairs, the clothes are further down the staircase. They couldn't have moved as they were stationary at the end of the other shot. (00:10:15)
Audio problem: When Norman is talking to his "Mother" on the phone, the camera (in Mary's point-of-view) comes in the room and Norman says, "How could you think such a thing. I would never do such a thing," but you can see Norman's reflection in the big mirror hanging in the lounge room and you can see his mouth isn't moving. (01:33:00)
Other mistake: When Norman and Mary are at the swamp, the sheriff hands him the ashtray they found and bates explains that it belonged to Mr Toomey. Mary say "Who"? and the sheriff explains who he is. This makes no sense as Mary knew full well who Toomey was and had no reason to play dumb.