In 1981, the US Department of Energy and the civil engineering company Bechtel Corp assembled a task force to help tackle the problem of how to warn future humans to stay away from radioactive nuclear waste sites thousands of years into the future. Perhaps the strangest solution came from the French author Françoise Bastide and the Italian semiologist Paolo Fabbri, who proposed genetically engineering cats to change colour in response to radiation, and creating a mythology of danger around those cats. An exploration of unusually creative problem-solving, the French director Benjamin Huguet’s film probes how the once-obscure, decades-old ‘ray-cat solution’ has recently found new life.