Patterns and other types of symmetric forms and structures are very often seen in inanimate matter too. The main principle behind the Navier-Stokes equation is Newton's second law, the basic law of mechanics. In fluids, this simple statement relating force and acceleration assumes a somewhat different form than in motion of rigid or elastic bodies but its essence remains the same. The physics of shape formation is relatively simple and can be illustrated by an example requiring only paper, glue, and scissors. Not everything that one can imagine can be obtained in a developmental process regulated by genes. Much like the thermodynamic and hydrodynamic processes behind cloud formation do not allow the formation of cube-shaped clouds with right angles, straight edges, and perfectly flat faces, genes can only regulate what is physically possible.