FWIW, this is a panel-by-panel illustration of a guy having his spinal reflexes popped for him. The guy trying to hold him down is actually potentiating his own reflexes -- by his own effort (equivalent to the Jendrassik maneuver ) -- which has the effect of amplifiying the magnitude of the reflexive response. The involuntary reflex action in his own body he ramped up to the point that the seated gentleman merely has to trigger the reflex arc and it pops -- like a compressed spring releasing faster (~25-50 ms) than his voluntary nervous system can even notice what has already happened (~100-200ms). Order of magnitude difference in latency of perception. This is not to diminish the art involved accomplishing that manipulation -- but it is why what you see is happening.