Back in America’s wild west, horses were the sole mode of transportation. In those days, cowboys had to do whatever they could to keep their horses from being stolen. It’s said that one cowboy had the idea of rigging horseshoes up to work as a lock. So as the story goes, that was the starting point for this puzzle. Don’t just use your head—you’ve got to wrangle with this one to solve it. The key word is "horses."