(Max Delbrück Center for Molecular Medicine in the Helmholtz Association) How do the cells of blood vessels decide between growing new side branches or expanding the surface? A new publication in eLife explains the mechanism and shows how the cells can behave as a collective, moving in the same direction together during blood vessel growth. The cells communicate using signals that exhibit oscillating patterns, as the scientists discovered using a combination of computer simulations and experiments. The findings are significant for diabetes and cancer.