Revealing mistake: When they drive out of Vegas, headed for Witch Mountain, there is a shot that appears to be made with a camera on a mobile cherry picker. The camera sweeps across the road and up high, watching as the vehicle passes under the camera. As it passes the camera, you can see a trail of dust that was kicked up by the cherry picker. It crosses the road and is still floating in the air from a recent crossing.
Revealing mistake: When the black guys shoot the four as they are about to enter the spaceship, watch carefully as the bullets hit them in slow motion. Because the camera moves backward slowly, the bullets move backward and then go forward at times. This is probably because the bullet animation is an overlay to the video.