When the Brothers are being chased by the Russians, Elwood tells Mack to look in the glove box. Mack says we've got carpet tacks, Elwood corrects him calling them drywall nails. When they're thrown onto the road though they really are carpet tacks.

Any carpenter will tell you drywall nails are about 3" long. what was spread across the ground sure wasn't long enough to be a drywall nail.