For humans, regrowing a lost body part would require superpowers. But for some other animals, it’s business as usual.

Salamanders are perhaps the most famous examples. If a salamander loses a leg or a tail, it can grow a new one in a matter of weeks. Golden apple snails can rebuild eyes within months. Some sea spiders can regrow their backsides in months, too. And those aren’t even the most extreme cases of regeneration. Some sea slugs can rebuild their whole bodies from the head down!

Scientists have long been fascinated by animals’ powers of regeneration. They want to know why some creatures can rebuild body parts while others can’t — and how these species pull off their feats of superhealing.

Recent studies have offered some clues. Salamanders, for instance, develop very slowly. As a result, adult salamanders may still have plenty of stem cells in their bodies. Stem cells can grow into many different types of tissue, making them useful building blocks for new limbs. Lungfish — which also develop slowly and can regenerate — may have a similar trick in their genes as salamanders.