Countless tiny hairs (cilia) are found on the outer wall of some cells, for example in our lungs or in our brain. When these micrometer-sized hairs coordinate their movement and produce wave-like movements together, they can cause currents on a microscale and thus pump fluid from one place to another. Until now, this could only be studied in large computer simulations. However, more than a few thousand hairs cannot be simulated in this way. Now a continuum theory of micro-hairs has been developed — a powerful and completely new approach.