Revealing mistakes: When the frat boys are sniping people with paintball guns, their paintball guns do not have hoppers, which hold the paintballs. While paintball guns can still hold up to 3 shots in the load chamber without a hoppper, they are unable to fire multiple shots in semi-auto as portrayed in the movie without reloading or using a hopper.
Continuity: During the pig stampede, when the old man shoots his gun he fires off three rounds. It is only a double barrel shotgun. The time in between shots is too short to reload the gun.
Revealing mistakes: When Kevin (Drake Bell) receives a message on his cellphone at the beginning of the movie, the alert reads "New Text Message", but when Kevin opens the cellphone a Video Message plays from his friend Carter (Andrew Caldwell).