A wolf pack switches from chasing prey to defending its den in an instant. Engineers have instilled this same versatility into an algorithm for a robot swarm. The key is a method proposed by John von Neumann: instead of chasing the target, the robots calculate its future moves and block escape routes, like beaters cutting off trails. Paradoxically, to catch the target, they often slow down: this reduces unpredictability and makes pursuit inevitable.

An internal guardian, a simple mechanism, ensures that in the heat of the chase, no one collides. By tweaking numerical settings, the swarm seamlessly flows from hunting to impenetrable defense. No reprogramming is needed: the swarm transforms on the fly.

Unexpected fact: the same principles are already used to analyze crowd movements: they predict crushes at stadiums and open emergency exits in advance.