Steve, those are called chrysals, those of us who work with bamboo get to see more than our share of them, when using a soft wood like red oak againsta bamboo back about all you can do is try to get as much limb workking as you can as evenly as possible. That bow is now scrap, sad to say but you got some good tillering practice in and did a pretty good job tillering it out. Don't feel bad, I had those little frets appear on several bows in december, all from the same jatoba board, nothing I could do would seem to avoid them. Steve