Table saw that stops when it touches skin

The video mentioned in the quote below is quite impressive.
I wonder how the detection of human skin works.
It works for the sausage, may be it detects the resistance the material is applying against the saw?

Table saw that stops when it touches skin: "Mark Frauenfelder:
I posted something about the SawStop table saw on Boing Boing a couple of years ago. It has a mechanism that makes the saw blade stop rotating an instant after it comes into contact with human flesh (watch the amazing video of it in action here). Kevin Kelly's Cool Tools has a review of the SawStop from a happy user (who has not had to test out the safety feature yet.)



(Via Boing Boing.)