Stone Creek Hair Stacker.
A Hair Stacker is a tool used to smooth out fur (deer, squirrel, etc.) before attaching it to your hook. It's extremely useful when used to tie tails, wings or heads of our flies.
It's as simple as putting the fur to the stacker, gently hitting a tabletop with it a few times and that's it. You now have ready to use, nicely smooth out fur.