So why might viruses care about our body clock? Since our cells are miniature factories, making things that the virus must have to copy itself, the virus is less likely to succeed when the production line is shut down. This is what we tested in the laboratory, by infecting cells and mice at different times of the day. We found that viruses are less able to infect in the late afternoon. In contrast, in the early morning, our cells are hives of biosynthetic activity, at least from the virus’s viewpoint. So, if a virus tries to take over a cell in the early day, it is far more likely to succeed, and spread faster, than if it encounters a rather less favourable climate in the evening.