When it comes to wiggling and writhing robots, I've seen a few. I've always enjoyed biologically inspired robotics, and even the most rudimentary of slithering mechanics can awake some kind of lizard-brain response that causes the hair to rise on the back of my neck.
There have been many methods of locomotion implemented to mimic the grip of a snake's scale or the track of an annelid's setae. I've seen wheels and I've seen bristles. I've seen them climb, and I've seen them swim. However, one particularly entrancing locomotion is new to me. At Case Western Reserve University, in the Biologically Inspired Robotics Lab, engineers have been experimenting with new methods of mimicking nature.
For this robot, they've created a system of hoops that are all controlled via a single rotating arm. The contracting and expanding motion could probably be explained as closest to that of an earth worm and may come in useful when needing to squeeze through tight spots. This system has improved the robot's speed, on top of the fact that the locomotive system is incredibly simple compared with others of similar capabilities.