From Denny: OK, these guys got MY attention with this nail bed demo. When I lived in Taiwan during high school I often saw interesting demos like this one from local martial arts experts during public festivals.
Here Popular Science breaks it down as to the physics and what they think it's all about. While part of what the science guys say is true there really is a spriritual component as well. Anyway you look at it, whew! Talk about an extreme sport!
"The Breakdown looks at the physics of a remarkable feat
Is this a death-defying demonstration requiring a level of mastery only arrived at after years of intensive martial arts training, or is it a theatrical display based more on physics than on chi? In order to answer that question, just take a look at the second video. Those guys haven't spent years in the dojo as far as we know, but they do know a little bit about fundamental principles of physics." - Popular Science
Just click on the title link to take you to Popular Science's article or go here.