Hmm.
Okay.
Well, how do you figure JFK's head and body went back and to his left like that?
Was he shot with a bazooka?
-- MWT
From my understanding, the bullet went through the skull and fragmented creating a wave of brain matter and internal pressure within the skull cavity which exploded the skull. From conservation of momentum (which follows from Newton's Third Law) the impact of the bullet on the rear of the skull would produce a small forward movement of the head, which it can be argued is seen in the Zapruder film. Equally, the explosion of brain matter would result in a movement of the head in the opposite direction. It is also argued that a neurological reaction (seen in experiments with goats I understand) could have contributed further to the back and to the left movement, causing a second movement. If so this, would mean a small forward movement, an initial movement back and to the left, then a further movement backward due to the neurological reaction. It can be argued that that is what is seen in Zapruder.
Bazookers are different types of weapons of course.