Continuity mistake: The stinger is deployed and is seen. Camera changes into the car and the stinger has vanished from the road. (00:09:20)
Continuity mistake: When driving to the pursuit, the cop in the passenger seat is putting his first glove on. Camera changes and now he has both gloves on. (00:08:25)
Continuity mistake: When the stinger is deployed it covers the whole road but in the front long shot it doesn't. (00:09:05)
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.