Revealing mistake: Dale threatens to shoot Shane, and Shane walks right up to him until the barrel of Dale's rifle is against his chest. Just before Shane walks up to him, you can see the imprint of the rifle muzzle on Shane's shirt from an earlier take. (00:32:50)
Revealing mistake: Merle is sitting in a chair and talking with Michonne and Andrea. At one point he takes off the prosthetic on his right arm to show them what used to be his hand (it's only a nub now), but shortly afterwards you can see his right hand in a fist as he puts the prosthetic back on. (00:13:00)
Revealing mistake: After Andrea avoids the truck on the road, she is attacked in the woods by some walkers and pinned to a tree. After breaking free, she goes to stab a woman on the ground with her knife. But as she goes to strike, you can see the actress slowing her strike down "pulling the punch" and gently resting the blade on the walker's head instead of actually striking. (00:20:41)
Revealing mistake: When Frankie and Tanya visit Eugene while he's playing the video game, he refuses to give them the pills he made. They call him a coward then leave, and in the next closeup of Eugene's video game screen we can see his reflection, but the problem is his reflection is not backwards as it should be (note his shirt buttons, etc). (00:44:10)
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.