(CNN) A cougar appeared to be stalking two cyclists as they biked over the weekend in the Cascade Mountains near Seattle. Suddenly, the animal charged, a survivor of the animal's attack that killed one told authorities.

The man said he hit the cougar in the head with his mountain bike, and the animal ran into the woods. But as he and the other cyclist were catching their breath and getting back on their bicycles, the animal returned and fastened its mouth on the survivor's head, crunching down, shaking the cyclist side to side like prey, King County Sheriff's Sgt. Ryan Abbott said Sunday, describing the man's account.

The cyclist managed to get loose when the cougar decided to chase his friend, who was running away, according to Abbott.

The two cyclists were attacked along a trail Saturday morning in North Bend, Washington, the King County Sheriff's Office said.

"It's an incredibly tragic story," Capt. Alan Myers of the Washington Department of Fish & Wildlife said Sunday. "It's extremely unusual for a cougar to act this aggressively on humans."

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