Revealing mistake: When Casper is pulled through the window with zombies hacking and chewing on her legs, her stumps end up as two clean cuts.
Revealing mistake: In the laboratory, one of the supposedly gray, rotting, skeletal zombies lying on a table has a very visible pink, healthy nose sticking out of its skull. (01:06:30)
Revealing mistake: During big gun fight to the house, if you watch in slow mo, a lot of the Zombies aren't attacking anything or anyone. They just appear to be running around randomly, or standing there like they're not sure what to do.