Factual error: At the climax of the movie, Alice swings the machete at Mrs. Voorhees and decapitates her. When the blade makes contact with Mrs. Voorhees' neck, her head flies off at an incorrect angle, as though the cut began on the opposite side.
Factual error: The first thing on screen after the opening credits is the year the film is set in, 1953. How then, do Kim Novak and Tony Curtis make their arrival in a Cadillac convertible, which is quite obviously of 1959 vintage? (00:19:44)
Deliberate mistake: Has there ever been a more obvious body double than the one used for Angie Dickinson in the shower scene? Not only does the top of every shot stop right at the collarbones, she is much taller than Dickinson, she has a much deeper tan and (of course) her breasts are much, much bigger. In fact that is Victoria Johnson, Penthouse Pet of the Month for August, 1976.
Continuity mistake: When the windows on Nick's truck are smashed, Elizabeth has protective gloves on when she covers her face from the glass, they are then gone when the truck comes to a halt.
Visible crew/equipment: When Harris and the two Irish men have been killed at the end and the car crashes on top of the other the ramp used to make it fly is visible.
Revealing mistake: During the scene in which Lou forces himself on Kim in the lunchroom, donning a black ski mask, Kim's brother Alex jumps up to his sister's defense. Just before Alex throws his first punch, Kim screams "Michael," referring to the actor's real name Michael Tough. Kim then correctly screams "Alex," the name of the character he was playing in the film.
Visible crew/equipment: When John is playing the piano, after the door opens by itself in the music room, there is a shot that revolves around him. If you look in the large mirror in front of the piano you can see the pole of the boom microphone reflected (behind the chandelier). (00:19:21)
Continuity mistake: In the last scene, the Butler and Groomsman load a Sarcophagus in the back of their station wagon. The tail gate is left open and both step back as the vehicle pulls out. As they are driving off down the driveway the tail gate is closed.
Revealing mistake: In this very-low-budget but star-studded flick about UFO contactees and cattle mutilations, Jan Michael Vincent's semi-auto handgun runs out of ammo during a firefight after firing only 3 rounds (the slide locks open, indicating the magazine is empty). Without reloading or racking the slide, Vincent continues firing 5 more rounds; but we see again, in close-up, that the slide is locked open, indicating an empty magazine. (01:00:55)
Visible crew/equipment: When the survivors of the cruise liner sinking approach the ominous ship, it's supposed to be deserted, but as a window opens, a person's arm holding a stick to open the window is visible.