Germy is clearly doing his job directing cars in the dusk, while Austin and Arlene are working during the night. They are obviously supposed to be working at the same time.
When Germy is looking at the pair in the car and throwing stuff in trash container, it's clearly still day, but when the pair is shown, it's clearly night.
When one of the policemen starts talking with Germy for the first time when Austin leaves, it's obvious they are all in different position than in the previous shot. Their position change in-between the following shots.
When Orville is seen at the drive-in for the second time he parks next to another car, takes a speaker and leans in to the window. Next shot of him he is not leaning to the window anymore.
The same shot of the manager lighting a cigarette, shaking his head, and walking into the projection booth is shown several times throughout the course of this film.
Catherine Barkley, who plays Jim's date, wears a brown wig in the film. When Jim attempts to remove her shirt, her blond hair is visible toward the back of her neck. She quickly grabs the wig and pulls it down.
When woman is killed at the start of the movie, fake skin when her neck is penetrated is apparent.
Ingleson obviously breathing when found dead in the car.
When man starts the car and woman's head falls of, her neck is not bleeding, which it would because she just got decapitated. There is also no blood in the car. Not to mention it would be almost impossible to behead someone who is sitting in a car and then put his decapitated head back like all is all right.