Continuity mistake: Sasha is pinned by the walker, but saved by Michonne. As she is standing up, the leaves in her hair disappear between shots.
Continuity mistake: At the end of the previous episode, Daryl leaves on a motorbike with a car following. In this episode Daryl's still out but no bike - he's in a car. It's a continuous trip with the bike he built at the compound.
Continuity mistake: At the end 3 men go to rush Rick - the guy on the right is Glenn. All three men are standing shoulder to shoulder when Rick pulls his gun, and Glenn has disappeared. Cut back to Rick and a wide shot - no Glenn. Cut to a close up of the group and Glenn's back, but there is a big gap between him and the other two men. This scene is continuous - he hasn't got time to move.
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.