Salamanders, specifically the axolotl, are vertebrates that can regenerate limbs and organs, which sure would be a useful technique for humans to have, too. So researchers, led by James Godwin, of the Australian Regenerative Medicine Institute at Monash University, figured out how salamanders pull it off. Godwin suspected that macrophages, cells that work in the immune system, played a part. When he and his colleagues removed the macrophages from the axolotls, the axolotls couldn't regenerate limbs: instead, they ended up with scarring and stumps. (A study on that was recently published in the Proceedings of the National Academy of Sciences.)