Clapper (I made my own out of a piece of maple 2" wide by 24" long. Had hubby cut it into 3 x 8" pieces and glued them together with Liquid Nail, sanded the edges and voila...cost all of $4 to make) Here's a video that shows how a clapper works:
https://www.youtube.com/watch?v=YsFy8wgHabQ