Sarah is an idiot... (spoiler)
In the scene where the teens get attacked by the zombies, Sarahs date is pushing the car, while Sarah is on the gas. Then the two chicks sees the zombies approach and yell for the guy to get out of there... But he can't hear them, because of the car engine.
So, Sarah, while trying to tell your boyfriend to get out of danger, why don't you let go of the *beep* gas so that he can hear you?