Place a one hundred dollar bill into a wooden holder. Ask a spectator to lock it in place with a padlock. The dollar bill remains visible at all times through 2 holes in the holder. Show 5 keys and explain that only 1 of these keys will open the lock. Whoever picks the correct key wins the money. Mix the keys up and ask four different people to each select a key. The choice is totally free. No force of any kind. Each person attempts to open the lock. Each one fails. You take the last key, insert it in the lock and it opens with ease.