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 reversed as it should be (note his shirt buttons, etc). (00:44:10)
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 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.
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.