The downstairs assumes that Marty is killed by Judah Buckner. However, an earlier shot shows that the downstairs is monitoring everybody's vitals, so they should have known that Marty survived the attack.
When Marty is attacked he is stabbed in the back by Judah Buckner - hole and blood stains clearly shown. When he is in the elevator with Dana it is clear there is no cut on his back - the shirt is whole.
"One Way" mirrors only work when the room on one side is very brightly illuminated and the room on the other is very dimly lit. In the cabin it looks like both rooms are equally dimly lit.
While in the "elevator" with Marty, Dana's bloodstains on the right side of her face completely disappear between shots.
During the tunnel collapse, Curt looks straight ahead for a brief interior shot, when before and after he is clearly hanging his head out the side window.
When the kids are swimming in the lake, a green towel appears and disappears on Marty's shoulders while he's standing on the dock.
When Dana is getting to save Holden by stabbing a zombie coming through a ceiling trapdoor in the chest repeatedly, as she backs away, you can clearly see she is holding a retractable stage property kitchen knife.
When Dana first enters the cabin she leaves the door open, the film cuts to Marty standing outside where we see the door close. When the scene cuts back to Dana the others are walking in through an open door.
When the rambler is at the gas pump, the football in Curt's hand disappears.
At the beginning of the movie, Jules shows off her new blonde dye job. When they are leaving for the trip she has dark hair roots.
When Dana is down on the dock after she escapes from the vehicle in the lake, one of the Bruckner men lifts her up over his head and throws her down on the dock. Dana is clearly a dummy with the legs somewhat bent at the knee and remaining frozen in that position the entire time. Once the dummy hits the dock and rolls once or twice, the camera angle changes and we see Dana on the dock pushing herself up after being "thrown".
When Curt is on his motorcycle there is a closeup camera shot of him and his hands. The motorcycle he is riding is equipped with a twist throttle and he is clearly revving the engine using his right hand, which would be correct. However, later in the shot he is shown revving the throttle with his left hand, which would be the hand the clutch is operated with.
When Dana is at the elevator main control station, the switches (for the individual elevators) on the control panel are inconsistently on/off between shots.
Bottles of beer are shown up to their necks in water in a cooler, and one bottle is shown being extracted from the cooler with water dripping from it. In the next shot when the bottle is tossed to someone, it is clearly completely dry.
Negra Model beer does not have a screw top closure. Sitterson can be seen drinking from the bottle, which would clearly require an opener.
When Marty supposedly dies early in the movie, he is stabbed in the back by a trowel. However when he appears later in the film, although there's still blood on his back, there is no wound.
When Jules makes out with the wolf, its teeth and jaw jiggle as if made of rubber.
When Jules is trying to having sex and open her shirt, her head is leaning right, but when the camera angle change, her head is leaning left. Also, Curt's hand is on Jules' stomach, but when the camera changes, his hand is on top of Jules' thigh.