I agree with Paul, I think most people see the impact of a bullet and the reaction of the animal as one movement.If you watch a slow motion video the two reactions are very noticable. Someone said something about a cement block , that is not flesh and bone , not to sound smart but that is alot of difference. I have shot deer with a .220 swift and up to a 45/70 and never knocked one off its feet like its being said, I would think a 45/70 at 30 yards 400 grain flat nosebullet at 1850fps would just about do it ,if it was possible.