The bouncing orange specks could be popcorn dancing on a hot plate. But theres something odd about how they move. Individual kernels spin in tight circles. Pairs slow dance a pas de deux. A cluster performs one full rotation counter-clockwise before dispersing. Each collision sets off a new motion. They seem to bebehaving.

What look like popcorn kernels inthis short videoare in fact a swarm of microscopic xenobots: tiny living robots, assembled from frog cells.

While living robots might seem a strange concept, in fact the first robots were made of flesh, not metal. Theword was coined in 1921, in a play by Czech playwright Karel apek.Rossums Universal Robotswas a thought experiment along the lines of Mary Shelleys Frankenstein, about a scientists desire to create artificial people. Nature has found only one method of organising living matter, declares Rossum, the scientist in question. There is, however, another method, more simple, flexible and rapid which has not yet occurred to nature at all.

Imagine him sitting over a test tube and thinking how the whole tree of life would grow from him, says another character.

In the century that followed, however, robots developed as things of steel and wire, rather than living tissue. Engineering moved faster than biology, says Douglas Blackiston, a developmental biologist at Tufts University. But biology is rapidly catching up. Blackiston is one of a team of scientists designing xenobots: tiny living robots, painstakingly constructed from tissue harvested fromXenopus laevis, the African clawed frog.

Thefirst xenobotswere revealed to the world at the start of 2020: minuscule cubes formed of skin cells and propelled by two stubby legs made of heart muscle. They were designed by a computer algorithm and hand-built by researchers with the objective to make the xenobots walk. (In a pleasing coincidenceXenopus means strange foot.) These organic automatons could also work together to move particles around their environment, and unlike mechanical robots they self-healed when injured.

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