Other mistake: When they are all on the beach and Simon kicks the zombie, which flips over and spits in his face. It hits his whole face, and some of his chest, yet later in the movie he has just one cheek effected by the "acid".
Other mistake: When the three rave survivors are hiding in the house, they don't even barricade the door. Alicia just opens the door and walks right in. You'd think they would have at least but the wood across the door like later in the film.