Continuity mistake: On the roof all the survivors are discussing their escape plan while T-Dog is lying down injured by Merle. In the next scene people are wearing rain coats and covering their bodies with the walker's remains as Rick proposed. T-Dog has taken off his cap and looks fine. Rick gives him the handcuff keys to free Merle. In the scene after, while Rick and Glenn went out the streets, the others go back on the roof to watch them from above. Nobody is wearing a raincoat and also T-Dog is in the same condition as before, lying down with his cap on. (00:24:00 - 00:31:15)
Continuity mistake: When the Winnebago breaks down. Shane and T-Dog offer to drive ahead to check out what could possibly be a gas station. Shane tells Rick to hold the fort while they're gone. Meanwhile Rick is dealing with dying Jim. When discussing Jim's predicament, Shane is there, he hasn't gone anywhere. Then when they put Jim under the tree T-Dog is there too. Then they all drive off like the breakdown never happened. Nothing is mentioned about whether Shane and T-Dog found a gas station and if they did, it was very quickly sorted out - two minutes tops. (00:31:00)
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: After they steal the car with the alarm blaring, there is a shot of the white van turning left down a road. It has just rained but the road is bone dry. A shot later there is water on the road.
Continuity mistake: As the scene opens on the rooftop with Daryl, T-Dog, Rick, and Glenn observing the area that Merle had been handcuffed to the pipe, blood splatter magically appears around the severed hand when it wasn't there at the end of the previous episode. (00:05:10)
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: At the end of the previous episode, the sun was setting but wasn't set fully yet. There was still a decent amount of light left outside as the door to the CDC was opened. At the start of this episode, as they are entering, it's already pitch black outside.
Continuity mistake: After Rick and Glenn cover themselves with guts, Rick tosses T-Dog the handcuff keys for Merle. T-Dog is at that moment in the rain coat and has on no hat, standing and appearing OK. The group then rushes up to the roof to watch Rick and Glenn on the street, and tell T-Dog to get back on the CB radio. Suddenly T-Dog is now leaned back sitting against the wall on the roof again with his hat and regular clothes acting all beat up again, and then shows Merle he has The Key.
Continuity mistake: Merle is handcuffed to a pipe and tries to seduce Andrea, saying they are going to die anyways. When she says, she'd rather die, his hands are apart closer to his sides, then when it cuts to a close up of him, suddenly he's got his hands together with one finger pointed at the other hand. (00:16:33)
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.