This astonishing GIF shows a microscopic chase scene: A black cell flees from the touch of a yellow cell, and the yellow cell goes after it.

On their own, the two cells go round and round. But if there are lots of them, the yellow cells end up corralling the black ones into long bands. And that, according to Hiroaki Yamanaka and Shigeru Kondo from Osaka University, is why zebrafish gets its stripes. In all of his Just-So Stories, Rudyard Kipling never imagined anything like this—an animal pattern that results from hundreds of cellular pursuits, played out over the landscape of a skin.

Here’s a longer video, complete with the most appropriate music I could find.

Kondo’s work has a long