How do cells work in a normal state? How do they change when they cause disease? Do they react as desired to new drugs? Nowadays, anyone seeking answers to these—and other related—questions in the laboratory can hardly do without a special technique: single-cell RNA sequencing, or "scRNA-seq" for short. This technique provides an accurate picture of gene expression in a single cell at a specific point of time, as well as the associated regulatory networks, allowing conclusions to be drawn about the molecular basis of cell activity.