Helen Brown drops a plate she is cleaning, and it smashes on the floor. She runs to the window to look outside, and when she steps back, part of the smashed plate is on the counter.
When the Browns decide to hit the road, the front door locks behind them. Later, when Brad reopens the door for everyone, he unlocks different locks.
Lee breaks off the patrol car's gear shift when first trying to learn to operate it. But, we later see them shifting the car into park and drive.
In the bowling scene, the pins in the lane to the left of the one that Ug uses disappears in the last shot of the scene.
When Ug transforms into Johnny Steele, you can see that when Ug reaches over to insert the "Earth Disc" prior to the transformation sequence that he is in human form already.
When Lee transforms into Reverend Miller, Jeremy Lawrence is obviously replaced by another actor at the podium.
At the end of the film when the sheriff drives the Browns back to the ruins of their farm, six people are seen riding in his car, three in the front seat and three in the back seat: the sheriff, the Browns, and presumably Charlie. But when everyone gets out of the car, Charlie is nowhere to be seen.
It is unsafe and against standard procedure to have the shotgun cocked and loaded in the police cruiser, although it does seem in character for Jeff.
When the rest of the family drags the father in through the front door of the house after he is attacked the second time, a crew member is very clearly visible through a window at the back of the shot.
When Harv drives away in his police car, the reflection of a crew member can be seen in the driver's side passenger window.
When Harv drives away in his police car (at approx 1 hr 20 min), the reflection of a crew member can be seen in the driver's side passenger window.
The image of Earth showing the Horn of Africa and the Red Sea is a mirror image.