Buy a small plastic bristle brush, such as that used to scrub dishes, from the Home Aisle at Walmart or Target. Remove the wood and scrub it with the brush. The bristles will be able to get into most of the cracks.
The wood will become smoother as if you were sanding it because you will be removing a layer of about 1/16 inch thick. Do the scrubbing while water is spraying or running over the wood, to keep debris from splattering all over.
This method works especially well on water-soaked wood. If you need to do this on a dry piece, then definately run water over it while scrubbing, as this will prevent the bristles from causing the wood fibers from raising up like hair. If this "hair" does not stop, you must soak the dry wood for two or three days, then scrub.