When you stroke the GeeHaw Whimmy Diddle, only stroke the notches in one direction. For example, press the second pencil against the notches and push it away from you; then lift it slightly so the pencils don't touch and bring the second pencil back towards you. Repeat this and the "propeller" should spin. To make the "propeller" spin the opposite direction, reverse the procedure. Engage the notches as you pull the second pencil towards you and lift it when you push it away. You can get the "propeller" spinning in one direction and then change the method you stroke it and the "propeller" will stop and then start spinning in the opposite direction.
Have fun and fool your friends!