(Stockholm University) Typically we consider that water molecules in the liquid state move randomly on ultrafast timescales due to thermal fluctuations. Now, scientists at Stockholm University have discovered correlated motion in water dynamics on a sub-100 femtoseconds timescale. This appears as 'caging effects' due to buildup of tetrahedral structures upon supercooling. The results, reported in Nature Communications on the 15th of May 2018 are based on a combination of experimental studies using x-ray lasers and theoretical simulations.