Flow of cerebrospinal fluid (CSF) within the ventricular system of the brain is achieved by cilia on the ependyma that lines the ventricles and is important for the transport of signalling molecules. Here, 1 μm fluorescent beads were used to track cilium-generated flow in organotypic cultures of the ventral part of the third ventricle. The authors found that cilia are arranged into distinct modules that beat coherently to control local flow of CSF in complex ways and across several hundred micrometres. This enables directed transport of molecules to specific locations.