Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advancements and more . CNN  —  A tiny creature with frilly gills, a polite smile and glowing green skin just gave scientists a major clue to solve one of biology’s biggest mysteries: limb regeneration. Aquatic salamanders called axolotls are known for their unusual ability to regrow limbs lost to injury or amputation. Now, researchers have uncovered more about the complex