When a backcountry camper strays off trail in Yellowstone, he finds himself in a part of the park where the usual rules don’t seem to apply.   The silence comes first. Then the tracks. Then the circling.   What stalks him through the timber doesn’t attack—not right away. It watches. It follows. It waits.   And by the time he understands what he’s dealing with, it’s already decided how the night is going to end.