What you’re seeing in this video is obviously a sperm cell, except it was made in a lab, not a testicle. It’s designed to show how passive elastic swimming can mimic, fairly well, the motions that allow sperm (or fish) to swim.
The video above is from a 2013 paper entitled, “Passive elastic mechanism to mimic fish-muscle action in anguilliform swimming.”
Oh, come on, “fish-muscle?”
Whatever this team of French scientists want to call it, it illustrates some interested dynamics. We can see the head of this “fish-muscle” bobbing back and forth. That’s because it’s a magnet driven by an oscillating magnetic field. The rest is specially woven filaments designed to be elastic—that is, to snap back into place as they are deformed.
As the head moves back and forth, its motion causes a wave to travel through the rest of the body. This wave drives the fake “fish muscle” through the water in what the scientists describe as “passive elastic swimming.”
Although the little fake sperm is easier to make than an active, undulating body, the motion isn’t as easy to recreate as it appears. One of the problems described in the paper is staying away from a standing wave. If you’ll notice in the video above, the motion moves through the body. Get the wrong elasticity or motion of the head and you might get a standing wave, in which there are stationary points, like this:
This will cause the swimmer to wriggle more and move forward less.