Where's the Beef?
Chigurh uses a mysterious weapon that blows holes in heads and door-locks alike, but it doesn't use a bullet. It's so scary, we don't even want to think about it for too long. Basically, it's some sort of air gun attached to a portable air tank. Easily concealed? Nope. But Chigurh doesn't care. He'll kill anyone who looked at him sideways, and he'll get away with it.
It takes a while for law enforcement (and us) to figure out what the gun is. Finally, Sheriff Bell asks about slaughterhouses: "How did they kill the beef?" (4.2.142). That's right, folks: Chigurh's weapon is the same thing slaughterhouse workers use to kill cattle. That tells us that Chigurh sees people as cattle; they're disposable.
Actually, he almost sees people as less than cattle—at least cattle are killed to eat. Chigurh just kills people who get in his way, turning the world into a slaughterhouse. You know you're evil when being a cannibal would move you closer to the good side of the spectrum.
The slaughter gun also points to the bigger picture, which is that the drug trade itself turns people into cattle and the world into a slaughterhouse. The violence it causes is impersonal, almost random. The sanctity of life is completely absent from this world. And that's a terrifying thought.