A simple ball of cells is the starting point for humans—and zebrafish. At the end of embryonic development, however, a fish and a human look very different. The biochemical signals at play have been studied extensively. How mechanical forces on the other hand shape the embryo is the subject of a study by Carl-Philipp Heisenberg, Professor at the Institute of Science and Technology Austria (IST Austria), and his group, including first author and postdoc Michael Smutny.