Revealing mistake: Before Paxton is hit with the 3 prong instrument, you can see the bloody holes already on his shirt. (01:01:20)
Revealing mistake: When the team descends to the bottom of a hole and one female member is first wounded and then dies. After checking her pulse, the others pronounce her dead and begin moving out. As the last one is leaving, the "dead" actress lifts her head up off the ground and looks left. (01:13:10)
Revealing mistake: When Stevie's car is hit by the delivery truck, the side shot that shows the car beginning to roll reveals there is no engine in the car, as we can see through the front fender wells to the truck as it passes on the far side of the car. (01:15:40)
Revealing mistake: When Gretchen turns around while on the bed, a shard of glass in the frame flaps in the wind.
Revealing mistake: When Jake "kills" Chelsea, and his phone starts to ring, the phone is blinking, and vibrating. It falls to the floor, and Jake reaches for it, when he does this you can see that the phone is not actually ringing, because the screen is dark and the screensaver is active.
Revealing mistake: When Chelsea is on the roof of the house and Kathy joins her, Kathy's hair is blowing in the wind, while Chelsea's stays perfectly still, the water in the lake is also perfectly still. Obviously the director had the actors do the scenes separately until we see them both together in which case both characters hair is blowing around. (01:27:40 - 02:00:00)
Revealing mistake: When Christina Ricci picks up the silver knife off the floor in her house and her hand starts to smoke, pay attention to the shadow. You can see smoke coming from her wrist before her hand touches the knife.
Revealing mistake: After Alex steps off the bus at the same corner as Camryn and Beth, some of the same extras keep walking past in quite a few of the following shots. Two examples are the woman wearing a striped top and black skirt, and the man wearing a plaid shirt and tan pants. (00:09:25)
Revealing mistake: When the group finds the picture of Daniel and his father Eric in the house, look closely at the photo - it was obviously very poorly patched together with photoshop. The lighting on Daniel/Eric does not match the lighting in the background at all, and it's clear that they have been crudely "cut out" of another photo and inserted over the background image. The extremely poor, obviously fake quality of the photo is even jokingly mentioned in at least one of the DVD commentaries. (01:01:05)
Revealing mistake: When Ben falls from the roof and into the leaves during the storm, you can see the mat that he lands on move from under the leaves.
Revealing mistake: At the beginning of the movie, when the guy is bitten in the wrist, if you watch and listen closely when he shoots himself, the blood comes out of his head before he actually shoots.
Revealing mistake: When Hayden is talking to the Psychiatrist in the Hospital, he is wearing some type of white powder face makeup to make him appear more "ghostly". This makeup was only applied to his face. Whenever they show a side shot of his face and neck during this scene, you can see the demarcation (line) of where the white powder face makeup ends and his natural darker tan neck begins. (01:05:20)
Revealing mistake: In the battle at the cathedral and at the end of the film when the footage is repeated, we see people hacking away at a torn up, dead body. The problem is their swords and axes are not damaging the body at all, revealing everything is a prop of some sort.
Revealing mistake: Towards the end when Sarah and Juno team up to find the exit, they pass underneath some thin stalactites. As Sarah goes under them, one of them wobbles as if it is made of rubber. In reality stalactites are rigid formations and are not supposed to wobble when touched. (01:26:40)
Revealing mistake: When Ryer and Rand jump off Rand's window and down to the street, they land on a tree. Notice the severed branches; instead of being broken [presumably from the falling bodies], they are cut rather smoothly.
Revealing mistake: When Chas is being thrown up and down between the ceiling and the floor, if you look closely as Chas is falling from the ceiling to the floor and goes up again, when he goes up it's just a rewind of him falling down. (01:28:35)
Revealing mistake: Katherine shoots Charlie twice to kill him at the end of the movie. Yet if you look at the chambers on the side of the gun, you can see all of them are empty.
Revealing mistake: When David goes to the house and picks up a bat to protect himself while walking through the house he is attacked from the back, and you can see his protective knee pads when he kicks against the wall, before he is suffocated.
Revealing mistake: Visible blood pack on the waitress's back when she gets stabbed by Otis.
Revealing mistake: When Charlie is climbing the wall you can see a handhold screwed into the wall when she lets go with her right hand. (00:59:45)