The video of the deer hit with an arrow is certainly not very clear. But from what I see, the buck appears to be reacting to the hit in the same way I've seen bucks and does react when shot with a slow heavy bullet in the heart/lung area. I have watched them fall down and try but fail to rise up. Perhaps in this case the arrow pierced the heart or cut one or more arteries which would immediately lead to a dramatic loss of blood pressure. Perhaps the arrow pierced one or both lungs. Either or both together would account for the confused reaction of the buck as well as its inability to stand up. JMHO. Sincerely. Brucev.