I was hid out in some brush earlier this year (the same place I killed a doe later), watching a heavily used trail. It was a cool evening without a breath of wind. I watched 4 deer heading my way on the trail; 2 does, followed by a small buck, with a bruiser taking up the rear. The does and the small buck passed by on the trail, 15 yards from my hiding spot, and never gave any indication of knowing i was in the same state. The big buck stopped on the trail about 60 yards away, turned around, and walked away. He didn't like something, although he never indicated that he saw or smelled me; just calmly walked away after following the other deer for a good way. I would call that a 6th sense in action.