J.C. is sitting on the toilet, trying to reach for the matches on the floor, which disappear as we cut to the wide shot from outside the booth.
In the tool shed, the flame thrower's pilot is unlit. Later, before Chris and Cindy go into the house, it's lit. In the house, Chris is holding the flame thrower and it is once more unlit.
When the Bradster calls, Cynthia puts the phone to her ear twice.
When J.C. first opens the door of his bathroom stall, there is no graffiti on the wall behind Mr. Miner's corpse. The graffiti appears when he emerges from the stall and crawls across the floor.
Considering the size of the Creeps, it makes no sense one would infest the body of Gordon since it wouldn't fit inside the cat's head.
When bus driver avoids a dog and crashes the bus, it's clearly a doll dog.
In the 28th minute, when making a sarcastic remark while investigating the lab break-in, Detective Cameron says "Whip Van Winkle" instead of "Rip Van Winkle"
A few things seen in the film's opening setting in year 1959, weren't yet made or existed.
During the scene when Chris and J.C. are confronted, one shot shows the second-unit AD clearly in the background waving towards people off camera to stay out of the shot.
After the re-animated corpse of the axe murderer has its head blown off, you clearly see one of the slugs being pulled away by a wire.
The heads of all of the infected zombies split open when the eggs in their brains mature into slugs and they spit them out. But the dog repeatedly spits out slugs and never dies after the incubation period.
Aside from the one frat boy who gets infested in 1955, nothing happens with the rest of the Creeps in the cylinder. They should have spread out looking for other organisms to infest.