Deliberate mistake: The cocaine dealer who was attacked by zombies returns after the group arrives. He is wearing the denim jacket he took off when the zombies attacked him.
Deliberate mistake: After the killer nails Shannon to the ceiling, he apparently has time to remove all the nails from the wall where he originally shot her, spackle, paint and clean up all the blood before the police arrive and examine the apartment.
Deliberate mistake: When Blade Abigail and Hannibal go to visit Dr Vance, Drake grabs Hannibal they move to a window, if you look behind them, the window is closed, then when Drake stabs Hannibal the window is open, then after drake goes out the window, you hear the window smash, even though he went out an open window. (00:56:15)
Deliberate mistake: When Alice first fights the Nemesis, she attempts to jump over a fence and make an escape. When she lands on the police car, Nemesis fires his RPG at her. If you look closely, the rocket passes magically right through a chain link fence without touching it at all. (00:44:40)
Suggested correction: Rocket made a big hole in the mesh. Clearly shown.
Deliberate mistake: In the first sequence, you see a man riding on the wooden battering-ram, and you can see where two different shots of the same man were spliced together, as the background suddenly shifts from being a forest, to being the exterior of the town, where the stone wall is. It was meant to be one single shot, but you can just see how the trick works. (00:00:30)
Deliberate mistake: When Tiffany is reading the self-help book for recovering addicts, there's a closeup of a page. While the headline for the chapter makes sense, the body text is completely unrelated and is about corporate work culture. (Likely just some generic free text the prop department copy/pasted into the book prop.)
Deliberate mistake: When Brody confronts and then flees from the Headless Horseman, the horses never break into full gallop (it's little more than a stiff-legged canter), which is odd for a life-and-death chase with the bloodthirsty Headless Horseman in murderous pursuit. This was probably done on purpose, for safety reasons, since the actor playing Brody was performing his own stunt riding at night. To cinch the illusion of a real chase, audio was added of a 4-beat gallop.