Continuity mistake: When April shoots the alien, they all go outside to look at it. Behind them, you can see the windows boarded up, but they don't board them up until later in the movie.
Continuity mistake: The car the hybrid man pushes is in OK shape at first, then he lifts and flips it through the copper fence, and now its whole front side is gone. They might used an already wrecked "car double" for the scene when it crashes and explodes. (01:40:50)
Continuity mistake: When the kids are looking at the Stonehenge-type structures, the younger boy calls for everybody to come and see the hidden message. From the shot in front of the boy you can tell from his body position he's sitting up, however in the next shot from overhead, the boy is now lying down on the rock.