From what I've seen, one of the differences between mature bucks and younger bucks and does, is that the younger bucks and does always seem like they have to verify two of their senses when they sense something out of place. They may spot something in a tree, they'll headbob, sniff and stamp their feet trying to get you to move. Where as a mature buck only needs one sense, and a small one at that, and he'll flee the scene. The big ones don't take any chances, that's how they get big.