"The Trouble With Tribbles" was an episode of Star Trek - Season 2 Episode 15.
From Wikipedia: "In this episode, the ship travels to Deep Space Station K7 to guard a consignment of grain bound for Sherman's Planet. On arrival, a trader named Cyrano Jones (Stanley Adams) gives Lt. Uhura (Nichelle Nichols) a tribble, with dramatic consequences. Kirk and the crew also have to deal with the arrival of Captain Koloth (William Campbell) and his Klingon battlecruiser, but the tribbles unexpectedly reveal a plot to poison the grain."