(at about one hour and 14 minutes into the film) When Orlok's car pulls up to the drive-in theater's ticket booth, the clock says 9:10. After talking with the two men at the booth for one minute or so, the car pulls away and the clock says 9:00.
(at about 11 minutes into the film) The outside of the Thompson's home does not match the layout of its inside. When Bobby pulls up in front of the house, the front door is set flush in a wall that runs the entire length of the house, yet when he enters it, there is a wall with windows running along the right side of the entry hallway that could not possibly coexist with the outside of the house.
The cost of an adult admission to the drive-in theater (posted on the admission booth in a later scene) is $1.25 for adults, but when Bobby buys a ticket, the change he receives from the ticket seller is consistent with a $1.50 admission charge.
The soda bottle's position changes several times between scenes as Bobby lies atop the oil storage tank to aim his rifle; also, the level of the soda in the soda bottle changes between scenes from full to nearly empty.
While Bobby is at the gun shop stocking up on ammunition, he is eating a Baby Ruth candy bar that stays its full length between scenes, even though Bobby is obviously eating it. This indicates several takes of the same scene.
Bloody bullet wounds, both entry and exit, are seen on Bobby's wife and mother, but no such wounds appear on the grocery delivery boy victim.
(at about one hour and 28 minutes into the film) At the very end of the film, the drive-in theater is empty the next day, except for the killer's car. This is illogical, since the victims' cars should be there, too.
When Bobby drags his mother's dead body into the bedroom after shooting her, she moves her head as he is arranging her "dead body" on the bed.
Bobby's check to the gun shop is dated late July, but when Orlok picks up a newspaper story about the supermarket massacre several days later, the paper carries a March date.
(at about 39 minutes into the film) As Bobby drags his mother's dead body to her bedroom, a camera shadow can be clearly seen moving up the wall and the door to the left.