The most popular guest characters to appear in the original "Star Trek" series spoke no lines. Small of stature and quite round in shape these life-forms made their lasting contribution to the Federation by eating, reproducing and, occasionally, by hissing at the nearest Klingon. Of all the beings ever encountered on the historic five-year mission, only this species managed to upstage the captain, and the entire Enterprise crew for that matter, by quietly being themselves. We're talking about tribbles, of course. Remember, they aren't just any furballs -- they're tribbles, the most fabulous furballs in the galaxy!