Embryogenesis—how an organism arises from a single cell—is one of the most mysterious and complex processes in nature. The large-scale, coordinated and collective movements of cells in a tissue during embryogenesis resemble the complex and chaotic flows of fluids in the ocean or atmosphere. But how do these movements determine which cells are destined to become part of the brain, the gut or the limb? If we could predict the fate of cells, we might be able to spot pathologies in the earliest stages of development.