Despite holding a lead heading into the final round of curling's mixed doubles match, the U.S. lost to reigning world champion Switzerland after the Swiss managed something exceedingly unusual: a perfect score known as a six-ender.

How rare is a six-ender?

Think of it as a hole-in-one in golfing, or a perfect game in baseball.

Although Switzerland was behind by one point entering the final round, Jenny Perret and Martin Rios had an advantage: the right to throw the final stone of the game. They managed to get their first five stones into the house. They then promptly knocked the Americans' lone rock out of the house.

According to the World Curling Federation, no curling team has ever managed a perfect score at the Olympics.