Continuity mistake: Arriving at Alexandria, Rick is shown from an interior POV leaning into the back of the car and picking up Judith, who is mostly wrapped in a spotty shawl. As he is shown doing this from an exterior POV, the shawl is barely visible, bunched up behind her legs. (00:41:44)
Visible crew/equipment: After Aaron refuses to provide his group's location, Rick tells everyone to eat and get some rest. When Michonne follows Rick outside it cuts to the car, and just as the camera pans to the right the actor's green nylon T-marker is visible on the ground, under the car door. (00:20:40)
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.