The project started with an accident. Four years ago, Steven Portugal was working at the University of Birmingham and studying how the colours and structures of bird eggs evolved. As he leant across his desk, he knocked over a large jug of distilled water into a box full of eggs.

“My first thought was: Oh crap, I’ve spilled lots of water,” he says. “My second thought was: Why does that one look so strange?”

On most of the eggs, the falling droplets flattened out and ran off in streaks, just as they would do on most surfaces. But on just one egg, they sat as a nigh-perfect sphere. As Portugal poked the egg, the drops ran off but kept their shape—spheres