How can a slinky be used to show waves are what travel on a water surface or in the air, and not the water or air?

A slinky can be used to prove waves travel on a water surface or in the air, not the water or air. To do this place a red dot in a slinky. The red dot represents a water molecule. When the wave travels through the water the dot oscillate up and down, the dot does not travel along with the medium. The waves move not the water. Similarly if the red dot represented an air particle, the dot would oscillate from side to side but not travel through the medium.