Audio problem: When Anton Chigurh challenges the gas station proprietor to a coin toss, at a certain point he says "It's either heads or tails." If you listen carefully it's clear that the phrase said by him has been dubbed.
Audio problem: When, at the end of the movie, Chigurh leaves the accident site after he said to one of the boys: "You didn't see me, I was already gone", the boy answers saying: "Yessir", but his lips don't move.
Suggested correction: The boy's mouth is open. You can say "Yessir" with your mouth open without moving your lips. Try it.