The axolotl is a Mexican mole salamander, about 15-45cm in length, and one of the cleverest critters you're ever likely to meet. If the axolotl loses a limb, it will grow another. If it loses a certain part of its brain, it will grow that back as well. Tests have shown that it will happily accept transplants from other axolotls, including eyes and portions of brain, and rewire them to work perfectly. Because of these amazing powers of regeneration, some axolotls swim about with several more limbs than are strictly necessary.