You're all fucking retarded, that is what needs addressed. You obviously have no Medical background or education in what happens when people get head shot and/or spinal cords severed. Any damage to the cord above his arms, where the nerve roots to said arms exit the spine, could cause that type of reaction. If you look into snipers that take out human bombs that have "Dead Mens Switches", they aim to sever the cord and or take out the brain stem at the base of the spine which causes that contraction, to keep the pressure from releasing on the dead man's switch.
Brain stem base of skull where the spine meets, mis typed