Continuity mistake: When the police car rolls out of the car wash, both passenger and driver's doors are open. When the shot changes to the deputy holding the rifle, the driver's door is closed. In the next shot both doors are open again.
Other mistake: In the scene where Judy and Becca are strapped to beds in the high school and the principal is coming with a pitch fork, at first there is a close up of the fork (when the principal is dragging it) and its dry with no blood, the principal walks over to his first victim and right before he raises the fork it is shown covered in blood so much that some has ran on to the floor.
Continuity mistake: When the principal stabs the 3rd victim (male) on the gurney, we see that the tongs on the pitchfork extend almost their full length underneath the bed. However as we see up top, the pitchfork couldn't have been that deep given it had the height of the man's chest to go through as well.
Factual error: Given the destruction from the nuclear blast threw the truck in the air, the rest of the surrounding area would also have experienced similar destruction. However when they are walking away from the truck to another town in a nearby field, there is no visible impact of what was a recent nuclear explosion anywhere to be seen.
Continuity mistake: When the sheriff is fighting the crazy underneath the truck and covers him in oil, the crazy pulls out a gun. When the sheriff initially ignites the oil the gun is missing, only to reappear when the crazy is completely on fire.
Continuity mistake: At the end when we zoom up from the Sheriff and his wife, the "spy satellite" view zooms significantly back but we don't see any of the telltale evidence of the recent massive explosion to the south of them that was seen in the distance while they were walking through the field.
Revealing mistake: At the end scene when the Sheriff is escaping in the truck away from the nuclear blast, the truck begins to flip through the air. While it is flipping we see under the vehicle and can see the hole they use to launch a post to help flip the vehicle for the stunt. A brief puff of white smoke also emanates from that hole briefly during the flip.
Other mistake: When the deputy pulls his gun on the sheriff, he takes the rifle and hangs it round his neck. In the next shot he's doing it again. (01:07:35)
Factual error: The movie is supposed to take place in Iowa in the spring according to the mayor who says they can't shut off the water because of farming, but says this while hanging out at his pool... in Iowa... in the spring...? BTW almost all farmers, and people in the country in general, have individual wells for water.
Plot hole: The water-borne biological weapon makes every individual a crazy murderer, right? Near the beginning a man burns his house with his wife and child inside. So then why do the three hunters not try to kill each other or the crazy wife in the nursery not try to kill her son?