When Dr. Gilmore checks the computer and realizes that Howard Johns was released by mistake, the information (list) on the screen completely changes in each shot.
Virgil's eyes would probably be red and bloody from spray he was sprayed with during the confrontation with Joan and the killer, yet they aren't in the following shots and he is functioning normally.
Although Susan is murdered, when her sister finds her, you can clearly see her abdomen move as she is trying to take shallow breaths.
When the killer is zapped by electricity and Joan runs away and the killer runs after her, he could easily see her behind cover because part of her body was protruding from behind the cover.
The woman playing Dragon's Lair is not actually playing the game itself and appears to be the laserdisc player hooked to the game's monitor and not the machine itself as the animation of the game is playing straight through, deaths and all. Also, the marquee at the top of the machine is lit up but the player's score display is not.
The film takes place in Upstate New York. There is a scene with a local news reporter who identifies his TV station with the call letters KTTN. A station in NY would have a call letter starting with W, per regulations set by the US government in 1912: Call letters for stations east of the Mississippi river start with W; stations west of the Mississippi river start with K.
There were too many people near the college when the killer catches a girl skateboarding the killer didn't cover her mouth, so somebody could hear her scream or see him.