When tramp is running from Lester trying to run him down, his surroundings change from shot to shot.
When Lester falls into the water while running, in the following shot when he reaches his car, he is already almost dry.
When Lester shoves woman's head into the oven, it melts, which wouldn't happen because her skin instead would start to get burned.
Woman mutilated with a chainsaw at the start of the movie is obviously replaced with a clearly fake doll when violence is shown.
When woman's feet keep popping out to stop the closing of the trunk, Lester cuts them off. They are both clearly fake not matching their look in previous shots and come of too easily when in reality he would need to saw them off.
Alice is obviously alive while in the car, squinting to see what Brett Halsey is doing to know when to do her part.
When Virginia calls Lester for the second time, the call comes to soon after the first one, while in reality she didn't have the time to call him again.