While conducting cancer research, Daley clipped holes in ears of mice that were genetically engineered with the Lin28a gene so he could quickly tell them apart from the control group. But the holes kept healing. So he clipped their toes, but they grew back. He then waxed their backs, but their fur grew back more quickly than usual. It appeared that Lin28a -- a gene that scientists think regulates the self-renewal of stem cells -- gave the mice special regeneration abilities.