Star Trek: The Original Series

Episode: TOS 042 - Trouble With Tribbles, The

Origin: unspecified. 
A small animal characteristically soft, furry, and pleasing to most humanoids (with the exception of Klingons). Tribbles give off a soft purring sound that is soothing to many.

They are also asexual, born pregnant, the only determinant of birthing being how much food they consume. The Federation first encountered tribbles on space station K-7 on stardate 4523.3.

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