Continuity mistake: After Beta kills Mary/Gamma, he drags her body and sets it up by a tree, dragging her by her hair. There is a jump cut as he walks away, and her eyes move to a different position, as well as the amount of hair over her face changes. (00:16:25)
Continuity mistake: Beta kills Marry/Gamma and places her next to a tree. During the scuffle with her, his mask was half ripped and another Whisper comes up to him, now recognizing his face. Beta kills the man, then the camera cuts back to Mary's body, and her head is now turned to the right and her hair has been brushed away from her eye. She also goes from being slouched over to nearly sitting up right against the tree. All this while she's just a dead body against the tree. (00:17:04)
Continuity mistake: Daryl and Carol are walking to an abandoned home. Carol walks by a bush with bright sunlight coming from the left of the shot. The angle changes and it's overcast with no sun. Then we see Daryl again and it's once again sunny.
Continuity mistake: The hole in the wall Carol makes with the knife grows, depending on what angle we see it from.
Answer: Walkers are attracted to noise, they can tell who's dead and who isn't dead, in S1 when Rick and Glenn cover themselves in walkers' guts they're able to get far by walking through the herd of walkers because they smell like they're dead, but as soon as the guts get washed off by the rain the walkers immediately attack them, if you draw attention to yourself they will attack you which we've seen that many times throughout the series that it's not always successful. Whether you're covered in guts hiding under dead corpses or under a car.