These comments from a seasoned neurologist, and good friend:
“A high-velocity projectile passing through the heart will cause an enormous (but brief) wave of over-pressure, instantly increasing blood-pressure in the brain and spinal cord to well above tissue-damaging levels.
Neither the brain, nor the spinal cord, can tolerate such high pressure!
The typical result is instant cessation of brain and spinal-cord functions.
High-velocity projectiles passing through the thorax, but not involving the heart directly, will have a similar (though usually not as dramatic) effect.
A violent wave of intra-thoracic pressure will intensely compress the heart, again sending a destructive high-pressure wave into the brain and spinal cord.
Either of the foregoing events will likely be lethal, but the “instant effect” you mentioned is caused mostly by the above-described pressure wave, and its effect on the brain and spinal cord.”
My comment: Assuming the good doctor is correct, the intensity and violence of this pressure wave is directly dependant on missile velocity.
Is the “threshold” velocity 2200 f/s, as I suggested?
I’m not sure we’ll ever be positive, but variances in post-impact animal behavior being observably connected with impact velocities are hard to discount.
/John