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.
I can't.
Other mistake: It would have taken two hundred $10,000 wrapped stacks of $100 bills to equal $2 million. There is no possible way that suitcase could hold two hundred of them.
Factual error: The satchel isn't large enough to hold $2 million. Maybe $1 million. There were six stacks showing on top, so $60,000 across the top layer. Each stack is nearly an inch deep, meaning that the satchel would have to have been about 30 inches deep, in other words 2 and 1/2 feet deep.
Visible crew/equipment: A crew member seen standing on the far left of the frame when Llewelyn is being chased down the river. (00:19:34)
Continuity mistake: During the dialogue between Moss and Wells at the hospital, there is an ashtray on the bedside table next to him changing position in various shots.