Tens of thousands of walkers, modelled on the slime mould Physarum. Each one only looks a few steps ahead and turns toward whatever trail is strongest, leaving a little trail of its own. The trail slowly spreads and fades. No walker has a map or a memory, and no walker can move into a spot another already holds. Yet together they grow a living web of veins that threads itself through the food sources and slowly reshapes itself as the trail shifts. Real slime moulds doing the same thing have redrawn the Tokyo rail network.