Some tell you that the only way to meditate is with your eyes open. Others say you should always close them. No doubt both are right – and certainly there are two ways of operating as a top-notch hammock naturalist. Today I was working with eyes open: knowing I could always close them if I liked.

I was staring at the green fronds of the ash tree, the soft grey of its bark and the sky above, busy clouds with occasional slivers of blue. And between me and the bark, a squirrel. Grey of course, or alas, but we must make the best of what we have, must we not?

It was ascending a branch that leant away from the main trunk at an angle of 45 degrees, and doing so from underneath. This was an overhang impossible to a human climber and on bark that looked dangerously smooth.

Yet the squirrel showed not the slightest sign of stress. Up he went. It was easy. Apparently. I watched, swaying gently in mid-air, my own defiance of gravity infinitely easier to explain. How did he manage it, then? And how would he manage the same trick on the way down?

The upward part is made possible by extremely sharp claws: claws that retain their sharpness because squirrels don’t spend much time galloping about on hard ground. The claws grip tiny cracks that would be useless to heavier and less well-equipped animal. Squirrels are also very well-balanced: that ensures an even distribution of weight on each of those sharp-clawed paws. No hanging on by a fingertip.

The downward part is about flexibility: squirrels can turn their back ankles through 180 degrees. They descend head down, toes backwards. It looks like magic: but it’s much cleverer than that. It’s evolution.

https://www.waterstones.com/book/how-to-fly/simon-barnes/9781526687548

https://www.amazon.co.uk/How-Fly-Taking-Insects-Humans/dp/1526687542