I have studied some Chinese martial arts, once upon a time.
For the record, I cannot perform this particular act. I was taught to NOT let that happen in the first place. However, it is also true that the masters can shrug off unbelieveable amounts of pain as though it were a mosquito bite.
I forget what they call the "Iron Body" training, but it is real. I studied the "chi sao" or "sticky hands" technique. Works fairly well considering I haven't practiced in years. This seems to be a demonstration of that Iron Body thing.
Note, I will remember what the term is as soon as I hit Submit. I will edit it in if that happens.
Brian
edit: Yep. the Iron body is called "Chi Kung". Or was it Chi Gung? Something like that.