Cat
A cat is a small, indestructible, furry automaton created by God to give you love and companionship when things fuck up your shit life. Nah, just kidding, nobody would love you, especially creatures who have some self-dignity. Contrary to popular belief, cats do not conspire at every possible turn to murder their owners and escape to the wilderness. Cats at times expand to fill all available space. (see Catsplosion)
Cats are accurately depicted in Dwarf Fortress.
An amusing consequence of the 3rd edition D&D system is that a domestic housecat is capable of demolishing first level commoners in combat, doing a point of lethal damage with a single bite or claw attack and being able to make two claw attacks and one bite attack in a single round. First level human commoners generally have between 1 and 5 hit points. However, longtime cat owners could testify that this is arguably realistic. For example, my ungrateful cat just scarred my hand, nyoro~n.