Walk with Me - S3-E3
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)
Walk with Me - S3-E3
Character mistake: When Andrea asks the Governor his real name, a young girl in pink shirt is walking like a "walker" and abruptly shifts to normal gait.
Suggested correction: She was never walking like a "walker." She was wondering around like many of the other extras. She looks like she was waiting for her family and when the boys approach, she stops wondering around and walks towards wherever they live.