whatThousands of bats pour out of a cave mouth that narrows to a gap a few wingspans wide, and instead of a pile-up the crowd becomes a smooth ribbon. The counter at top right stays near zero collisions.

whyReal bat streams do this every dusk, with no traffic control. The piece shows how flow becomes laminar when every individual only wants to keep going, keep its distance, and fly roughly like its neighbours.

howEvery bat wants three things: to keep going toward the far end at its own preferred speed, to keep a wing's length from anyone else, and to fly roughly the way its neighbours fly. Walls and obstacles push back when close. Click to drop an obstacle in the corridor and watch the ribbon split around it and knit back together.