The axolotl had enough cool stuff going on without the cute factor, so that dopey grin is just a bonus. This Mexican amphibian has the extraordinary ability to regenerate not only limbs, but vital organs like the brain and heart. If they lose an eye, you can just dunk a new one from another individual in there, and the axolotl will use it as if it's just borrowing a hoodie. Unfortunately, as of 2013, the axolotl is most likely extinct in the wild. But its amazing powers of regeneration have made it a popular pet, and it lives on in captivity.