A few years ago, the axolotl became a craze when everyone wanted to own one as a pet or wanted merchandise sporting these water dogs, so-called in the native Nahuatl language. They have several characteristics that make them unique in the animal kingdom. First of all, axolotls are actually amphibians but never actually go through metamorphosis. Secondly, they’re able to regenerate limbs that they’ve lost completely. They can completely regrow an entire leg in just a few months, complete with nerves and muscle tissues, making the regrown limb completely functional. They can even regenerate tissues of the eyes and heart, as well as less vital parts of their brains.