Thanks, glad you like it. I use a trim nail as a mandrel. I've never had a problem. The file in this video is a Xacto file, I'm not sure if that's the same as a jeweler file. Feel free to ask any questions that you may have.
Big Epp I can answer your question. That material is deer hair, which is hollow. When you cinch the thread down on it the hair flares out. You start tying at the rear of the hook. After you tie in each bundle of hair you pull all of the fibers straight back or pack the hair then wrap the thread in front of it. Continue this process all the way up the hook shank placing each bundle of hair directly in front of the last. Finally you trim the hair to shape.