For no apparent reason, just beyond bow range, the buck stopped. He licked his nose--the classic behavior of a whitetail trying to smell just a little better--and his body tensed. Then he took a single, hesitant step backward. Game over, I remember thinking. The buck never gave any indication of what he'd detected, but his confident stroll morphed into a slinking retreat--and he was gone like a vapor. Why? It's the question behind a long-debated topic among hunters: Do deer have a sixth sense, an innate ability to detect danger even when the five known senses seem beaten? Many hunters dismiss the idea, arguing that whitetails like the one I mentioned above nail us by some stray molecule of scent, whisper of sound, tic of movement unreadable to us but clear to the deer. But the debate has been renewed of late thanks to, of all things, natural disasters and combat.