A Slinky is a coil that climbs down an incline. The motion of the coils are a good model for the motion of an earthworm.
First the front slinky coils stretch forward, and then rear coils are pulled forward.
The video shows different ways that a slinky can move. Note that you have to get the slinky started, and then the force that keeps the coil moving is gravity. This means that a slinky best moves down an incline. Test a slinky and see how the angle of the incline affects the speed of the slinky.