whatA slime mould explores a dish, joins its food sources with a network of veins, then prunes the network down to the few links it needs. Click to erase a patch and the veins reroute.

whyPhysarum, a single cell with no nervous system, designs transport networks that engineers have compared to real rail maps. It shows how a good network can be found by growing everywhere and then keeping what is used.

howThousands of agents each sense a trail field at three points ahead, turn toward the strongest, step forward, and deposit trail where they stand. The field diffuses a little and decays. Food deposits trail of its own. A fan of exploration collapses into veins that join the food, and the sparkline counts the loops the veins enclose, falling as the network prunes while every landmark stays joined.