They are mythical creature from an old comic strip from the late-1940's and 1950's called Lil' Abner and they became a cultural icon during the 1950's.
Basically, schmoos constantly produced milk and eggs and reproduced like crazy, and if you looked at one with hunger, it would die from sheer joy at being useful and they could taste like any meat you wanted depending on how you cooked them. However, schmoos were declared a menace to the economic well-being of the world because they produced a near limitless supply of food requiring almost nothing in return which made people lazy.
