Continuity mistake: When the trailer is being dragged by the bulldozer, the wheels rotate. The trailer would need an air hookup to make it happen, otherwise, the tires won't rotate.
Continuity mistake: When Burt and Heather are fighting the graboid in their basement, shortly after Heather yells "Magazine!", one of the large revolvers between them falls off the rack but is replaced in the next shot.
Visible crew/equipment: As the camera pans up to the roof of Bert's house, a film crew member is reflected in the window.
Revealing mistake: When the last explosion happens after Val tosses it, what looks like detonating wire coming off to the left is visible for a few frames.
Continuity mistake: After Burt reports on the radio that he has killed the graboid in his basement, there are shots of the towns people celebrating. The sky behind all of them is different, specifically the mother and her daughter. In other shots there is blue sky. In these shots there are darker clouds.
Revealing mistake: When the graboid goes to launch out of the side of the cliff, you can see the wall is fake because it moves in and out right before it breaks through.
Revealing mistake: Given that the store is a set to move up and down to simulate the graboid attacking it, we can actually see the store's brick walls bouncing in the shot before the effect was used.
Revealing mistake: After the lawnmower flips over, the camera angle from behind it shows the steering mechanism that's attached to the front wheels would not be on a normal one.
Continuity mistake: In the beginning of the movie, watch Kevin Bacon's hair when they're driving in the truck. In some camera shots, his hair is blowing in the wind. In others, his hair is not moving at all. This happens several times.
Continuity mistake: The green fuzzy dice in the guys' truck change over and over. Sometimes they're stuck up behind the rear view mirror, sometimes they're hanging down. Granted, they could fall and the guys could stick them back up again, but in one scene when they're behind the mirror, the faces of the dice that are visible from the front change.
Chosen answer: The machine is a vibrating case cleaner, which is used to polish the brass casings of pistol and rifle ammo. The "dirt" is actually an abrasive polishing compound.
BGraz