Researchers have captured how a molecule redistributes energy after absorbing light, differentiating the roles of individual atoms in the process. They used X-ray flashes from the European XFEL to show that different atoms in the same molecule can reveal different aspects of the process. The study provides evidence that excitation by light can enhance an atom’s sensitivity to the motion of nearby atoms. The new method for following ultrafast chemical reactions at the atomic scale, in real time, can help researchers understand photostability in DNA, energy flow in light-harvesting materials and other fundamental processes driven by light.