A good night’s sleep isn’t always as restorative as we think. Researchers at England’s Medical Research Council Laboratory of Molecular Biology wanted to find out how skin wounds heal in tandem with the body’s circadian rhythms, the 24-hour clock that defines the body’s regular shift from being sleepy to wide awake. Every cell in the body has its own biological clock. And because these clocks can survive outside a living organism, scientists just had to collect some skin cells from mice and humans, damage the cultures, and watch them repair over the next few weeks. Watch the video above to see what they discovered, and the implications it may have for clinical practice.