Visible crew/equipment: When Paul pokes the dead body with a stick, you can see a diver's arm turning the corpse over.
Other mistake: The Blazer was only hit twice by the baseball bat, once on the right front fender, and once on the grille, but it sustained a massive amount of damage. Also, when the infected guy was inside, throwing up blood, you could see that the windshield was cracked in several spots, but it was never hit.
Continuity mistake: When Marcy leaves Karen's side to confront Jeff, in the first shot Karen's blanket is tucked under her legs. But in the next shot, her blanket is lying loose upon her mattress. Also, leaves that are bunched up at the side of the mattress disappear between shots. (01:00:50)
Answer: Sticking her finger up his bottom. I believe it is mentioned in one of the commentaries.