Visible crew/equipment: At the start of the movie when the teens are heading off to the woods in the Jeep, in one of the backseat shots, you can clearly see a cameraman in the rearview mirror. (00:04:00)
Continuity mistake: When the kids are in the shop near the beginning of the film, at the shopkeepers desk is a cardboard box, and next to it are some jars and tins. Between a couple of shots the jars/tins rotate and move position on the desk, and also two or three jars/tins appear then disappear. (00:07:30)
Continuity mistake: When Karen and Paul are on the raft, they are laying down talking. In a specific overhead shot Karen's arm are by her sides, but in the next shot they are folded over her body. (00:13:50)
Revealing mistake: When Marcy and Jeff are having sex, at one point Marcy rolls over on top of Jeff. When she does this, there's a couple of instances where you can see a red cord from the bikini bottom she's wearing to preserve her modesty dangling down in the background. (00:14:05)
Continuity mistake: When the blonde goes to kiss her boyfriend as they are floating on a platform in the lake, she rolls herself off the platform and completely submerges herself underwater. When she comes up for air, it cuts back to her boyfriend looking at her, then back to the blonde who is head above water and her hair is completely dry. (00:14:20)
Continuity mistake: When Bert is out shooting squirrels, he has a bottle of beer in a brown glass. But when he starts the fireplace up, the bottle is green. Also in certain shots as he drinks from it, it's clear the bottle is empty. (00:14:50)
Continuity mistake: When Bert returns from shooting, he talks to Jeff and Marcy, when returning his BB gun hangs over his right shoulder. Shot changes and his gun hangs over his left shoulder. When it cuts to the last back closeup of him and as he walks away to the cabin, you can see the gun has jumped to being over his right shoulder between the shots. (00:17:00)
Continuity mistake: When Paul begins telling the story of the mass murder in his town's bowling alley he says the alley was called "Lenny Mead's Brighton Bowl". But when we see the flashbacks of the massacre, the business name embroidered on the employees' shirts is "Black Sky Bowling" (00:19:00 - 00:21:05)
Factual error: A doctor is seen using a syringe to inoculate the individual with the disease. It is clear that the containment gloves and sleeves he is using are not proper as you can see his skin between the gloves and the sleeve. If this were a real containment unit his entire skin would be covered. (00:31:00)
Continuity mistake: When Bert and Jeff find the crazy woman who is gutting the pig, when she first starts yelling at them, there is blood all down the side of her protective goggles, but then suddenly it all disappears and her goggles are completely clean. (00:31:20)
Continuity mistake: When Deputy Winston is talking to Paul, he takes his tinted glasses off, in his left hand. Then in the next shot he has them in his right hand, although he never swapped hands. (00:38:05)
Continuity mistake: When Marcy, Bert, Jeff and Paul are in the cabin talking about the fact that maybe they should prepare their own meals, during the conversation before the scrap between Jeff and Bert, watch Marcy who's sitting on the couch. Between shots she goes from having her hands up in the air, to folded or down in her lap. (00:52:00)
Continuity mistake: The cabin interior doesn't fit with its exterior. In the interior shots you can see that the front door opens in to the main living room, with a window beside it. Next to this window is a doorway to the main bedroom. In other shots, we see that this bedroom also has a window on that same wall. In the exterior shots, there is only one window on this wall, and the cabin's length is nowhere near long enough to fit two spacious rooms. (00:54:40)
Continuity mistake: When Bert first realises he has the fever, he crouches beside the car and starts coughing up blood. When he hears the others coming he wipes his mouth, leaving a small trail of blood on his chin, but when he stands up and talks to them the blood is gone and his chin is clean. (00:54:55)
Revealing mistake: When Marcy cleans Karen's face up after Karen had vomited blood, the paper towels she uses don't absorb any of the blood, and stay pure white. (01:00:50)
Continuity mistake: When Marcy leaves Karen's side to confront Jeff, in the first shot Karen's blanket is tucked under her legs. But in the next shot, her blanket is lying loose upon her mattress. Also, leaves that are bunched up at the side of the mattress disappear between shots. (01:00:50)
Continuity mistake: When Marcy and Paul are talking about their hopeless situation "being like being on a plane that's going down" you can see a small wall hanging to the left of the glass panel door in the background. Also, the shadows from the hanging and door frame cast left, away from the door. Later, when they have sex in the same bedroom, the wall hanging is on the right side of the door and now its shadow casts towards the door. It's definitely not the opposite wall of the room, as this is shown earlier and has a wood-plank door, a much larger painting mounted on it and unlike the wall shown in these scenes, it isn't wallpapered. (01:01:35 - 01:02:30)
Continuity mistake: When Paul and Marcy start having sex, Marcy's hair is running down her back. Paul asks Marcy about whether they should use a condom. Cut to a close-up of her face for her reply and her hair is suddenly hanging over the far side of her face. Cut back to the original angle and her hair is running down her back again. (01:02:30)
Deliberate mistake: The sex scene between Paul and Marcy is broken up with a shot of Karen dying alone in the toolshed. The shot is well-lit, but we saw Marcy closing the door when she put Karen back in the shed, leaving the shed virtually pitch dark. So where is the light coming from? (01:02:35)
Answer: Sticking her finger up his bottom. I believe it is mentioned in one of the commentaries.