Factual error: Season 5 and they are still driving cars around! Gasoline won't last years unless specially treated.
Other mistake: Most if not every time someone kills a walker in close proximity or repeatedly bludgeons one that is already dead with a blunt object and there is a CGI blood spatter effect (as opposed to a practical blood spatter effect), the blood magically never gets on the person's face.
Other mistake: In the opening scene when the cop stops at the side of the road & walks between the truck & car you can see there is no engine or transmission on the truck lying on its side. (00:00:20)
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)
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)
Factual error: Ten minutes into the episode, where they're setting up their police-blockade, a cop makes a remark about being in some TV-show when Rick Grimes replies with: "Make sure you've got a round in the chamber and your safety off". Next we see the first cop checking his gun (a Glock) for a round in the chamber and we see him flicking his thumb across the gun's slide catch: not a safety-lever. Glocks don't have an external safety, so the cop cannot flick a safety-lever like in the episode. (00:10:10)
Visible crew/equipment: When the car flips in the chase scene, you can see the round canister used to flip it. (00:10:25)
Revealing mistake: As the first gunman is shot in the chest you can see the square patch from the blood pack. (00:11:20)
Factual error: The supposedly American tank Rick crawls into in Atlanta has US markings but is a British Chieftain.
Factual error: The grenade Rick finds in the tank has an unpainted body and a blue safety lever. It's a dummy training grenade. (00:06:20)
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: 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)