Pretty much what's already been said. I've had to mix a lot of dubbings and have a few coffee grinders that I've picked up at yard sales for about $1. each. Do Not make the mistake of using your coffee - coffee grinder or you'll most likely get he** from wifey. Anyway for natural dubbings: beaver, muskrat, rabbit, mink, fox, mole, even seal, etc. I'll just cut the fur/hair at the base (remove guard hairs for dry fly dubbing) and spin it. You MUST USE very short bursts of the grinder otherwise the fur can get cut. For synthetics I generally cut the fibers at about 3/8 to 1/2 inch. I believe the trick is to not use a lot of material at one time and again, you Must use short bursts otherwise heat will build up and melt the fibers. Rmember, whether using natural or synthetics, every so often wipe in and around the grinder blades, dome and sides with an anti-static tissue or towel that you've sprayed with some type of anti-static guard. Yes, there are other ways to prepare dubbings but I find this is the easiest, fastest, cleanest and least messy way of doing it. But do get yourself your own grinder!
Hope this helps.
Allan