My dad and I had something like that happen to us once, a couple seasons ago. We got lucky and found two trees a few feet apart that could each hold a climber. We were sitting up there when something passed by VERY close. We hadn't seen anything, and just kind of forgot about it. A few minutes later, it happened again, this time from behind. It came in and clipped a twig a few inches from my dad's head. It kept on going, and when it landed on a stump twenty yards out, we got a good look at him. Great horned owl (it's amazing how silent they are). We were wearing all kinds of camo, and all the evidence of food that thing needed was a little movement.