Luca Tubiana

Take a long thread, close it into a ring, and tie a knot in it. The knot slides along the thread until it hits something. Now imagine the thread is made of two different segments: one stiff and slippery, the other soft and sticky. When heated, the sticky segment softens, and the knot can slide off it, like a sled sliding off a melting hill.

An octopus waits with tentacles spread wide. No central controller directs its arms, but the moment prey touches one, all eight wrap around it. Physicists have recreated a similar trick in the lab with a body that has neither neurons nor muscles: a star polymer with self-propelled arms. The polymer was assembled from small cylindrical vibrobots on a vibrating plate.