This was the subject of one of the lectures I took in Biophysics at the TU Delft in the Netherlands, great to see this talked about. A lot of our intuitions abo

This was the subject of one of the lectures I took in Biophysics at the TU Delft in the Netherlands, great to see this talked about. A lot of our intuitions about motion is based on the old swimming idea of "I'll kick a vortex of water backwards and it will propel me forwards!" and that simply doesn't work if you can't exceed this critical force of the fluid, which is what you need to do to make vortices and transfer out of a laminar regime. Instead you have to essentially "crawl along" the fluid around you, rather than "swimming" in the normal sense. Another lecture which was memorable dealt with the sheer variety of different situations and biomechanisms which you can rule out using the Second Law of Thermodynamics. The bottom line is that when you're at thermal equilibrium then everything must jitter thermally by the same amount, which is what excludes "Brownian ratchets" [1] from working: if you peek inside at the spring and asymmetrical "teeth" inside an actual ratchet, then you realize that the work extracted actually comes from heat-transfer to the spring, which is being implicitly assumed to be at 0 temperature in the naive "oh, you get energy out of nothing!" argument. It's a very simple 2nd-law argument to make, but really hard to poke around inside and figure out what's going on internally. [1] https://en.wikipedia.org/wiki/Brownian_ratchet https://en.wikipedia.org/wiki/Brownian_ratchet