Rat Dogs

Origins
Rat dogs are aliens previously thought to be a crossbreeding between rats and dogs (like Chihuahuas NOT CRICKET!!! [inside joke.]) It was recently discovered that they were in fact aliens. They were stranded on the planet Earth when they attempted to escape from human vision using Frustration Teleportation. Their ship teleported, but they did not, stranded in the middle of the first crop circle.

Psychology
Rat dogs exist only to impede, irritate, and inhibit. Their warped outward appearance was shaped through centuries of doing this to each other. They are also ferociously courageous until confronted with real danger (i.e. a bigger dog) They believe their piercing yaps disguise their tiny size, but they really just confirm what you think it is (a rat dog.)  Thy also tend to live in large, wealthy homes — they think themselves humungous, ferocious beasts.