I have been obsessed with these for years and have never seen one in person. They are more sophisticated than I thought! The little ones work on simple biomechanics like you'd expect, but the big ones, as far as I could determine, actually include hydraulic digital logic -- like, there's a proboscis with a flat foot next to it, and when each is compressed it closes a valve. 00? Waving in the air. 11? Hard ground. 01? Soft ground, reverse gears. The +5v analog(ue) is a series of water bottles pressurized by the wind and some valves.
But it's all just so weird that I doubt he realized he was building logic gates and a Turing machine. If I were a biochemist I might read this as reaction-diffusion interactions or enzymes. Or if I was a psychologist, I'd think it was id and superego.
These things are glorious.
PS: I tried to make this post from my phone and it basically rolled on its back and wiggled its legs in the air because apparently sending a 63 MB email to my own damned mail server is unreasonable and this is not the future I was promised. What the what.