Pretty Much Dead Already - S2-E7
Other 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, and then subsequently fires two shots at her head. She should have dropped, as ANY blow to the brain kills a walker instantly. However, she is still moving until Shane dramatically moves right up to her and shoots her in the forehead.
eaglegrad16
Chosen answer: They saw Rick run off with Carl and Michonne.
MasterOfAll