Revealing mistake: Each crew member has a monitor on their spacesuits that they use whenever they are exploring the caves. Whenever the monitor is shown, each crew member's individual heartbeat is shown in the lower left corner of the monitor. But no matter which heartbeat is shown, every time a heartbeat on the monitors is shown, it is always the exact same heartbeat, despite the various changes in panic and stress throughout the movie.
Revealing mistake: When we see a vision of Child-Alyssa walking down the street with a sort-of vortext behind her as the cult-members flee, watch closely and the entire shot is comical. All of the extras are barely moving at a jogging-speed despite supposedly running for their lives from her. Several are visible running towards her direction or even directly behind her despite supposedly fleeing from her. Several extras veer off to the side before exiting frame even though there are buildings on either side so there's nowhere to go. And several others still are visible running left-to-right or right-to-left from either side of the frame, again despite there being buildings on either side. Obviously all of the extras were filmed in front of a green-screen being told "just run around a bit" and then added to the scene. The shot makes no sense if you pay attention.
Revealing mistake: Right at the end of the fight between Selene and the Uber-Lycan in the vampire coven, the Uber-Lycan throws Selene into some wooden panels, knocking her unconscious. As she travels through the air you can tell that she is suspended by wires; she travels far too slowly towards the wooden panels for someone who was just thrown. (00:48:35)
Revealing mistake: When Arthur goes into the marsh to bring Nathaniel's corpse up, each time he emerges to get air, you can see the lack of mud around his lips from an air mask.
Revealing mistake: When Sparky's tail pops off there is a hole where it popped off. But when the tail goes into the bucket the hole is gone.
Revealing mistake: When Alice shoots the zombie in the blue dress, we get a frontal shot of the gun. Pay close attention to her trigger finger: it doesn't move at all, while the gun does fire.
Revealing mistake: After The Corpse first gets back out of 'hell', he saves a girl from some zombies in sleeping bag-like sacks. As they jump towards him, the animation is bad and they flicker around on the ground like a game glitch. (00:11:30)
Revealing mistake: When Wyatt is in Katie's house we can hear him call his sister's name, however he says Kathryn, which is the actress that plays Alex's real name.
Revealing mistake: IChat is used to make a second call to Professor Jonas, only this time we can see Professor Jonas is online under "Bonjour". Without too much detail this would mean that Professor Jonas is in the same house (on the same LAN) as Ellison. (01:31:55)
Revealing mistake: When Three Finger is driving the truck to ram the car containing Angela's husband you can see round the eyes that it is a mask being worn.
Revealing mistake: When Ray reminisces about having fought the Germans in WW2, a flashback is shown with him fighting in a bunker. He is carrying a No.4 Lee-Enfield rifle which requires the bolt to be worked after every shot to reload. However, he is shown firing two shots in rapid succession without moving his hands at all, revealing the shots to just be flashes added after filming.