Pretty Much Dead Already - S2-E7
Revealing mistake: When Shane lets loose on the gang at the barn about the two walkers Hershel and Rick just brought out from the woods, he fires several shots into the female walker's torso, as he screams at Rick about them not being human. Then subsequently fires two shots at her head. Yet she is still moving when she should have dropped. As ANY blow to the brain kills instantly. But she doesn't drop until Shane dramatically moves right up to her and shoots her in the forehead.