The board game Monopoly served allied prisoners as a real-life tool to get out of jail during World War II, says Brian McMahon in Mental Floss, a magazine devoted to intellectual esoterica.

In 1941, the British Secret Service asked the game's British licensee John Waddington Ltd. to add secret extras to some sets, which had become standard elements of the aid packages that the Red Cross delivered to allied prisoners of war. Along with the usual dog, top hat and and thimble, the sets had a metal file, compass, and silk maps...