When struck this pressure points is struck there is an immediate, violent and dangerous response from the brain. The blood pressure will drop quickly causing a "vascular faint" or knockout. This can be accomplished with a low to medium strike.
A harder strike can cause serious damage to the nervous and arterial systems of the area which will result in death. ST-09 is also Dim Mak points because an energy strike to this part of the system, both nervous and vascular, will cause enough "dysfunction" to result in death overtime.
Carotid Sinus Reflex:
The serious martial artist should be concerned about Carotid Sinus Reflex when it comes to this pressure point and ST-10. The effect is temporary loss of consciousness or a knockout that sometimes accompanies convulsive seizures. This is because of the power of the carotid sinus reflex when pressure builds up in one or both carotid sinuses.