In propaganda, the ‘Labels’ one use has a powerful effect. The “Magic Bullet Theory”. The “Violent motion” of JFK’s head. Choice and establish the right labels and you have won half the battle.
If you can establish, in people’s minds, the motion was “Violent”, maybe not possible by JFK, maybe not possible for an Olympic athletic, then what else could cause this motion but the powerful effects of a bullet?
But if the motion is actually much slower, much more ordinary, then maybe something more ordinary could account for this motion, like the muscles of JFK’s body.