Dubbing is simply coating your thread in bees wax or dubbing wax (I make my own). I use bees wax mostly. Pinch a bit of dubbing material and role it on between your finger tips. If your doing a small dry fly you would want to role it on tight to the thread, if you want a "buggy" looking nymph you might loosely role on bigger bundles and pluck out legs later with your bodkin.
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Sen. Hillary Clinton - Speech at Democratic Fundraiser, June 2004