Until recently, many people outside of Australia had never heard of thequokka, a Muppet-cute (despite its beady eyes and rat's tail) marsupial with an irresistible smile.

But this week, people's selfies with the furry critter (its name rhymes with mocha) have charmed the Internet. So what's the story behind the quokka, whose chronic grin earned it the moniker "happiest animal in the world" a couple of years back? (See pictures of quokkas submitted to National Geographic's Your Shot.)

First off, the animal, preferring thick vegetation, inhabits island swamps and thickets off the coast of West Australia—mainly on Rottnest Island (map) and Bald Island—as well as eucalyptus forests and riverbanks on the mainland.

These social plant-eaters hang out in clans, munch on swamp peppermint and