Revealing mistake: We see a close up of the money in the truck and the $100 note has got "This bill is for motion picture use only" printed on it. (00:05:40)

Revealing mistake: Agent Lang takes a picture of a debit card inside the first victims car which is a clearly prop. The name is "Jane Doe", and the card number is 1234-5678-9101-1112. (00:05:40)
Chosen answer: "Policing your brass", means to pick up your expended shell casings, after firing your rifle, or pistol.
pross79