Here's a mysterious animal fact: The axolotl, a type of salamander, has the incredible ability to regenerate entire limbs, its spinal cord, heart, and even parts of its brain without any scarring. Despite this, it remains in its juvenile form throughout its life, a phenomenon known as "neoteny," where it doesn't undergo the typical metamorphosis that most amphibians do. Scientists are still trying to fully understand the mechanisms behind this regeneration.