The naked mole rat, or sand-puppy, is an amazing (and completely real) little creature that lives its entire life underground and is only found in East Africa.  As mammals go, it is exceedingly odd. For starters, it is one of the handfull of mammals known to be eusocial - aka, each colony is ruled by a queen and has drones, just like termites and ants.  Their huge teeth actually grow out through their lips so they can use them as digging tools without getting dirt in their mouths. Their blood is specially adapted to deal with oxygen deprived environments (like deep underground).  They don't seem to be able to get cancer, and their dna is leading to advancements in cancer treatment. On top of all this, THEY DON'T FEEL PAIN. Seriously.  The chemicals necessary to send pain signals from the skin to the brain simply don't exist in these little guys - they don't respond at all to heat or acid.  Almost so ugly that it's cute, the naked mole rat is a pinkish little wrinkly ball of amazing biological science!