French manicures and finding the end of the sticky tape; if this is all you thought fingernails were good for, think again. A new study explains why our nails are crucial to our natural ability to grow back lost finger, and even provides clues as to how we might enhance our limited powers of regeneration. Although we might not be able to grow whole fingers, we can regrow the ends of amputated fingers. For years, scientists have wondered why this only happens when some of the nail is left behind. But now the answer has been discovered. Studying mice, the biologists found stem cells – cells that can change into any other kind – in a layer just below the nail on mice toes. When the very tip of a toe is amputated, a chain reaction is initiated that draws nerves to the area. This in turn prompts the stem cells to form new bone tendons and muscle. If a finger is amputated too far back and there is no nail, this chain reaction does not get started. It is thought that the same mechanism is behind the regeneration of human fingertips. “If we could identify all the molecules that have this special ability to induce this kind of regeneration, a pharmacological approach to treat amputees might become available,” says the researcher who led the study.