Continuity mistake: Reba gets out of their truck at the compound and looks through the binoculars - in the foreground you see the tractor and trailer they use to escape are very close together, or are attached already. When Kevin Bacon and the other guy figure out to use it, the camera pans around and the tractor and trailer are 60-100 feet apart.
Continuity mistake: When Val and Earl are relaxing with a couple of cold ones after they bury the trash, Val's recliner chair changes. From the side it is a brownish-rust color cloth material. In the next shot, from the front view, it is greenish leather. This scene takes place after Rhonda's near miss with the graboid but before the first guy, old Edgar, is found dead.
Revealing mistake: When the graboid starts pulling Jim underground, his wife hands him a board to keep him above ground. You can see the thick board bend rather easily while his wife hands it to him. Also when Jim is sucked under ground it bends quite easily as well, as if it were styrofoam.
Factual error: When Val is talking to Burt on the CB radio and desperately trying to tell him to get out of his basement, Burt is using a handheld CB. After Val's very last transmission, Burt is now holding a rifle, not the CB. When the Graboid crashes through Burt's basement wall, we hear him say over Val's CB, "Jesus Chr..." his transmission was cut off. First of all, Burt wasn't holding the CB so he wasn't transmitting at the time. Second, there are portable CBs that you can lock the PTT button for extended transmissions (I owned one), but that wasn't the case here. Finally, even if by some chance Burt accidentally did lock the PTT button before putting it down, it wouldn't have cut off. The Graboid broke through away from where Burt was standing and talking and couldn't affect the CB. It was done for dramatic effect of the scene. (00:58:30)
Continuity mistake: When Val is getting the fuse lit on his bomb to throw to the last Graboid, we see his hands separated, one holding the bomb and one holding the rope. The camera angle changes to a close up of his hands, where they are now both holding both the bomb and rope. (01:24:50)