When a kid lops off a fingertip with a cleaver or car door, there's a chance the end of the digit will grow back. The fingerprint will be gone, and the tip may look a bit strange. But the flesh, bone and nail could return.Doctors have seen the effect in humans without quite understanding how it happens. "Kids will actually regrow a pretty good fingertip, after amputation, if you just leave it alone," says Dr. Christopher Allan, from the University of Washington Medicine Hand Center, who wasn't involved in the research.The orthopedic surgeon saw this out a few years ago when an 8-year-old girl stuck her finger into the spokes of her brother's bike. The wheel sliced off her middle finger, near the nail cuticle, and her parents rushed to the ER to have it sewn back on.Allan specializes in hand reconstruction, but he couldn't find the tiny artery he needed to reconnect. So he opted instead for what surgeons call a biological dressing. Just stick the tip back on and hope for the best, he says."The girl came back in a few weeks with the old fingertip in a bag and a new one on her hand," Allan tells Shots. "It was far better than anything that I could have given her with a graft or surgery."