John Jensenius, a NOAA lightning safety expert, explained to The Verge how a single lightening bolt could decimate more than 300 reindeer: Though lightning strikes typically kill only 10 to 20 animals when they hit a herd, a lightning strike on July 18, 1918, in American Fork Canyon, Utah, killed 654 sheep. Jensenius says that although animals do huddle together during storms, they don't have to be touching to conduct a lightning bolt's electricity. Instead, he said, ground current—the spreading of energy along the earth—is the real killer. In the case of the Hardangervidda herd, ground current—which travels up one leg then down the other of animals or persons within proximity—killed every reindeer in a 50- to 80-foot diameter. Animals are especially susceptible to ground current, Jensenius added, since their legs are farther apart than humans', so the current travels more easily inside their bodies.