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#50: Star Trek: The Original Series, season 2, episode 15 "The Trouble with Tribbles"
Written by David Gerrold, directed by Joseph Pevney.
Stardates 4523.3 through 4525.6 (July 2268)
"Well, the nearest thing I can figure is that they're born pregnant." - Doctor McCoy
The Enterprise is approaching Deep Space Station K-7, which is right on the border of Klingon Space and within range of a planet in dispute between them and the Federation, when K-7 issues a Priority-1 distress call. Captain Kirk orders the ship to race the rest of the way to the station. Only, once they arrive, Kirk doesn't find a battle, but a bureaucrat named Nilz Baris (William Schallert) flexing his authority and demanding Kirk's men guard a shipment of special grain designed to grow on the disputed planet. Kirk grits his teeth and tries to appease Baris while giving his crew shore leave aboard K-7 when a Klingon battleship appears. But instead of fighting, they insist on using K-7 for shore leave as well. Now two rival crews must share the same station where a shady character has merchandise to sell... including a fuzzy little creature called a Tribble.
Originally released: 29 December 1967
"The Trouble with Tribbles" on Memory Alpha (mirror)
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Visual effects comparison of the original broadcast & the Remastered versions.
https://www.youtube.com/watch?v=9hAeM6PxAjM