This stick seems to be magic. When another stick is rubbed across its notches, the little propeller at the end Spins. When it is rubbed differently, the prop turns in the opposite direction.

One explanation:

"The variably generated vibration frequencies and harmonics thereof react in concert upon the main body of given mass and configuration to set up vibration patterns and nodes which agitate the essentially statically balanced and frictionless rotor into rhythmic rotational movement."

How to operate the The Whimmy Diddle

Grasp the notched stick in your left hand and keep the notches to the top. Hold the dowel in your right hand, curling your index finger over the end of dowel. Rub the tip of your index finger along the left side of the notched stick, below the notches, as you stroke steadily from one end of the notched area to the other and back again. When your index finger applies some pressure against the notched stick as you rub the notches, the propeller will turn to the right (clockwise). Try to rub the notches with the dowel in a steady rhythm, back and forth. Keep your right thumb off of the stick.
To reverse the direction of rotation, lift your index finger away from the notched stick slightly and keep it from making any contact with the notched stick. Apply pressure to the right side of the stick with the tip of your thumb as you continue stroking the notches in a rhythmic way. It may take a few minutes’ practice to get the pressure and speed right. Never have both thumb and index finger touching the notched stick at the same time. Always use just one or the other.