Biathlon is a punishing sport that mixes cross-country skiing with shooting. Competitors ski up to 4.7 miles per stretch and then squeeze off a .22-caliber rifle shot at a small target 50 meters away – timing the shot between heartbeats to steady the gun, the way military snipers do. The teams to beat are Norway – which once trained its soldiers this way – France, and Russia. In order to test the depth of each nation's pool of athletes, rather than just individual stars, the new team version is made of two women and two men.

What to watch for: For each shooting round, there are five targets and eight bullets, though the last three are loaded manually, which can take eight seconds. If a shooter fails to hit all the targets, he does a 150-meter penalty lap.