Tremors (1990)

Revealing mistake: When the lawn mower the heroes send off as a diversion crashes you can see a wire pulling it. (01:01:30)

Revealing mistake: Near the end, Val, Earl and Rhonda are way off the rocks after the blast. When the monster comes up out of the ground and Val takes off, you can see the "ground" bounce. It's definitely a false ground so they can get the "graboid" pushed up through it. (01:24:10)

Revealing mistake: When the horse is lying on the ground with the tentacle wrapped around it, you can see a wire to the left of the screen attached to the horse. (00:31:00)

Mortug

Revealing mistake: As the last Graboid falls off the cliff at the end, just before it hits the ground, you can see its skin has already been cut up for the "blood" to gush out of upon impact. (01:25:20)

James Ollier

Revealing mistake: When the graboid starts pulling Jim underground, his wife hands him a board to keep him above ground. You can see the thick board bend rather easily while his wife hands it to him. Also when Jim is sucked under ground it bends quite easily as well, as if it were styrofoam.

RJR99SS

Revealing mistake: When Earl and Rhonda are being chased into the store and they're running along the little boardwalk, the boards are forced up like a wave by the snakeoid. But the ground under the boardwalk is perfectly flat.

Krista

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.

jerimiah

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.

jerimiah

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.

jerimiah

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.

manthabeat ★

Revealing mistake: When Dr. Jim and his wife are backing away from where the generator was, you can see the ground behind them is flat. When it cuts, there is suddenly a pile of sand on the ground. This pile is hiding the hole that Jim falls into. (00:23:35)

Mortug