Revealing mistake: When George and Nick are walking across the street from the hospital where the "guy in the cowboy hat" is recovering, you can see that there was a green screen being used. As they are walking across the street, they seem to be a different shade than the background and a couple seconds later, George is hit by the ambulance.
Revealing mistake: In the hospital scene when the nurse is filling the tub for the patient in the room above the cowboy's, he leaves the water on. When the water starts to come out of the tub it is coming out many times faster than it is going in.
Revealing mistake: "Death" sets up Hunt's demise by activating the pool's purge pump and running it at maximum (so powerful it can suck the internal organs out of a person). The purge pump runs for several minutes before Hunt drops his coin into the water and goes after it. Despite the purge pump running at maximum all that time there is no change whatsoever in the pool's water level.
Other mistake: In the scene were Lori, Nick, and George are all congratulating themselves at cheating death right after George tried to kill himself. When they pour the cider into the glass, just watch the amount of cider in George's glass it constantly changes.
Continuity mistake: When Hunt is about to leave, right before he says he'll check on Janet, the back of his shirt is tucked in, but as he exits his shirt is no longer tucked in.
Revealing mistake: In the first shot of the custom car shop, a nozzle can briefly be seen spraying showers of sparks (supposedly from welding).
Revealing mistake: When Nick has his arm nailed to the wall behind the cinema screen, he sets off the sprinklers to put out the fire. After this he sits back down again, at which point his "nailed" arm and hand move slightly (an inch or two). This would not be possible under the circumstances.
Visible crew/equipment: In the hair salon if you look into the mirror on the left as the camera moves, you can see the camera in shot.