What is the Trisula and How is it used?
The Trisula is a tool / technique taught by Guro Inosanto through Steve Tarani. It has applications which when used correctly are very effective. It’s basically a flesh scraper. You use the back edge to ride up the side of the forearm, filleting the flesh from the bone. When the back edge of the knife hits the elbow, your hand will flip the knife to the primary edge and sever the triceps. 

Or another way: Picture stropping a knife, the spine of the knife is going away from you (trisula edge) when you run out of leather on the strop, instead of flipping the knife
and stropping it the other way, you continue to cut in the same direction with normal edge. The elbow forces the trisula edge to stop, but the momentum will allow you instead of stopping, to pivot the knife and continue cutting.

And yet another description: I have my knife in my right hand, thumb up and off of the handle. I trap BG's right wrist in between the back of the blade and my thumb. (Kind of like chopsticks my right hand thumb is one, the back of blade is the other). Slide the back of the blade up inside of the arm up, digging in as you go (filleting), when it hits your elbow bone, there is still upward momentum, so the blade flips (picture a bike going fast and slamming on the front brake) the edge then continues up cutting whatever is in its way.

MSC SMF Nightmare Recurve w/ Trisula (left), DDC SMF Chisel Ground Droppoint w/ Trisula (right)
(Photo by HKSIG45)


Example Trisula Technique
(Photo by Hank Greenberg on USN)