An axolotl is hard to call cute, exactly. Paired off in rows of numbered tanks in a Harvard lab, the pale salamanders look out with pinprick eyes, and feathery red gills wave at each end of their wide smiles. Their primary appeal to scientists such as Jessica Whited, an assistant professor with the Harvard Stem Cell Institute, is their shocking ability to regrow not only severed limbs but also to repair damaged internal organs such as the heart, lungs and ovaries.