Exercise Wheel

When I was a child I raised gerbils in my bedroom. I also had a ten gallon fish tank and a windowsill terrarium made out of a mayonnaise jar on its side. I remember the gerbils would run on the wheel in their cage and it would squeak so I would put vaseline on the axle to silence it. I imagined it would be funny for humans to get exercise by running in place on a wheel. Now they do!!