The axolotl (say "ax-oh-lot-el") is a Mexican species of salamander. It's also known as a Mexican walking fish. It can regenerate, repair or replace its arms, legs, tail, lower jaw, brain and heart.

For axolotls, it may take only a couple of days to regrow their tiny hands, but in a fully grown human, that process could take years, McCusker said. “It’s important that we continue to do ...