Continuity mistake: When the deputy sheriff comes out of the house, her ink pen is sticking through the hole in her pocket flap but not in the pocket itself. After she turns around at the car, her ink pen is inside her pocket and not "flapping" loose as it was just a split second before.
Continuity mistake: In the scene where Merrill, Graham and the kids are returning home from town, and Morgan is holding his baby monitor to listen to the aliens, his fingernails are very long. When he gets out and climbs on top of the car to get a better listen, his fingernails are very short.
Continuity mistake: When they first see the crop circle, Graham takes one step into the area, and the rest of his family crowds behind him, still basically in the corn. In the next shot (arial shot), supposedly right away, Graham is about ten steps into the circle, while Morgan and Merrill are about six or so.
Continuity mistake: In the scene where Morgan is explaining what the aliens would do if they were hostile (when Morgan, Merrill, and Bo are wearing tin foil hats), Merrill is seen hugging his knees in a closeup shot. In the next shot, Merrill has his hands on top of his knees now, instead of hugging them.