Last summer, Zac Peterson was on the adventure of a lifetime.
The 25-year-old teacher was helping archaeologists excavate a 800-year-old log cabin, high above the Arctic Circle on the northern coast of Alaska.
They had pitched tents right on the beach. Over the course of a month, Peterson watched a gigantic pod of beluga whales swim along the beach, came face-to-face with hungry polar bear, invading their campsite, and helped dig out the skull of a rare type of polar bear.
But the most memorable thing happened right at the end of the trip.
"I noticed a red spot on the front of my leg," Peterson says. "It was about the size of a dime. It felt hot and hurt to touch."
The spot grew quickly. "After a few days, it was the size of a softball," he says.
Peterson realized he had a rapidly-spreading, skin infection. And he thought he knew where he might have picked it up: a creature preserved in the permafrost.