T is for Tribble

Spock: [while holding a tribble] Most curious creature, Captain. 

Its trilling seems to have a tranquilizing effect on the human nervous system.

[beginning to pet it gently] Fortunately, of course, I am... immune to it's effect...

[realizing what he is doing, he quickly puts the tribble down and excuses himself]

Tribbles (Polygeminus grex) are small, non-intelligent lifeforms originating from Iota Geminorum IV. Known for their prodigious reproductive rate, these round, furry creatures emit cooing sounds while touched, which have a tranquilizing effect on the Human nervous system. Born pregnant, a single tribble with sufficient food can quickly increase its number exponentially through presumably asexual reproduction, bearing an average litter of ten every twelve hours. On their homeworld, tribble populations are kept in check by a large number of reptilian predators. 

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