This The SAW robot (Single Actuator Wave-Like Robot) produces a pure wave motion using a single motor. It’s 3D Printed bot not only can craw crawl, it also can climb and even swim.

This mini robot copies the movement of snakes so it can move across irregular surfaces. SAW can also travel as fast as 57 cm/s [2.5in/s] on a straight path.

Ben-Gurion University of Negev designed SAW for rescue operations and medical procedures.
The robot could even be built small enough slither into your body for medical use purposes.