National Treasure - Mixed-Up Nail
During the scene when all the characters are in the huge underground cave, and when Ben (Nicholas Cage) is hanging from the broken board, look at the nail. It is circular, and has a shine in the metal. In the time of our founding fathers, the nails were cast square, so it was easier to make. And the metal wasn't shiny, it was dull, because they didn't need to take the time to refine the ore.