In the 23rd century, an enterprising trader named Cyrano Jones procured an interesting and adorable little creature. These tiny furry beasties had a calming effect on the nervous systems of humanoids - well most humanoids, anyway. They were called tribbles.
These tribbles, when they're not busy being cute and purring, were prodigious breeders. As one country-doctor once quipped, "Well, the nearest thing that I can figure is that they're born pregnant - which appears to be quite a time-saver!" In fact, their ability to multiply is so incredible, they can fill an entire cargo hold in three days - that's one million, seven-hundred seventy-one thousand, five hundred sixty one tribbles... assuming one tribble with an average litter of ten producing a new generation every twelve hours. That's some impressive breeding, right there. It would make any man want to high-five any tribble, except tribbles don't have arms.
These tribbles, however, are genetically altered to be sterile. In fact, ThinkGeek will guarantee that, should their tribbles somehow begin to multiply, they will dispatch someone to remove the infestation from your starship or space-station - even if it takes seventeen-point-nine years.