rydra_wong suggested that it might be gua sha or the Graston technique -- on googling, both look to be pretty much the same thing, and they both look like what he did to me. It was kinda freaky -- like I had rice crispies he was popping under my skin! Apparently the metal tool sliding over the skin pop and squashes mini-dots of scar tissue in the muscle and just smooths everything out. I can't wait to talk to the chiropractor about it.