Revealing mistake: Carl is walking toward a walker embedded to a tree. In the background there's a female walker wearing a distressed white dress with long black hair and a bear trap caught on her leg, standing in the back waiting for her scene to walk out. (00:22:30)
The Day Will Come When You Won't Be - S7-E1
Revealing mistake: When they pick up Glenn's body, for a brief moment, you can see his head is fully intact.
Revealing mistake: When Rick checks his revolver before holstering it, there are no primers in his cartridges.
Pretty Much Dead Already - S2-E7
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: When the Governor is hunting Andrea, he smashes a few windows in the building where she's hiding. When he breaks the first two, there's a jet of steam or air, showing that it was broken a split second before he hit it with the shovel. (00:29:04)
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)
Revealing mistake: When Aaron is pinned down by the sewer zombie, the zombie actor's neck can be seen below his head mask.
Suggested correction: I went back and watched this scene several times, and I think the OP is mistaking Aaron's hand on the Walker's neck as the gap in the mask.
Revealing mistake: When Carl rolls out the knife pack he found, the scene cuts to Shane working on the engine, and you can see traffic on a highway through the bottom of the windshield. (00:33:00 - 00:34:00)
No Sanctuary - S5-E1
Revealing mistake: When Sam has his throat slit, the location of the wound does not correlate with where the blade was shown to be slicing the skin.
Revealing mistake: After it starts raining there is a shot looking at the road in The Distance. Notice how the rain is only falling in a small area and stops just beyond where the group is at. The road is dry from there on out.
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)
Hostiles and Calamities - S7-E11
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 Morgan stabs the walker which is hanging from The Tower, the blade enters its lower head, but the blood can be seen coming from above the hairline. (00:25:30)
Suggested correction: I can see where the confusion is. If you watch it normal time, it looks like he stabs him in the cheekbone. But in slow motion, you can see the blade go into the top of the skull.
Revealing mistake: Near the end of the show, while Rick is still in Atlanta (he is on a secondary paced road), you can see vehicular traffic moving on a bridge in the background.
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.
Suggested correction: Those two shots were actually into the torso. He fired three into the torso, paused, two more into the heart and lungs, paused, then two more into the torso before he put one in the head.
Revealing mistake: As the first gunman is shot in the chest you can see the square patch from the blood pack. (00:11:20)
Revealing mistake: When the two cars drive down the freeway with the cable in-between them, there is no blood or body parts on the cars at the end despite the carnage, suggesting CGI effects.
Revealing mistake: One of the saviours goes to shoot Carol but Morgan shoots him first, about 4-5 times. The man goes through the motions of being shot and we get a good view of his body/chest area and head, but there are no bullet holes.
