I have shot abut one out of three deer as head shots across a lifetime of hunting. Over the last fifteen years I started shooting for just the brain stem. I did this because often enough a brain shot lets them flop and lash around which can get you messy when you shoot them right under your stand. Brain stem shots seem to stop all that pretty well. I have observed in maybe1/3 to 1/2 of the brain stem shots that after a couple minutes legs will sort of male a slow walking type movement. Usually only one or two legs, and only one or two "steps". The way it's been timed, I suspect it's just the muscles running out of oxygen. I have never sen a brain stem shot deer lash around.
I think 9 seconds is about it with a fatal heart/lung shot from a rifle. A little more for arrow shot deer. For shots that drop blood pressure to zero instantly that in my experience has allowed a run of up to 200 yards. The hardest to get my head around was one that made it a little over a mile after I put an arrow (4 blade broadhead, 3 inches of cut and all 4 blades did open on the way in) through both lungs and bled so well I could follow the blood as fast as I could walk. Sometimes you don't get the expected result or a means to explain what you did get.
