Capt. Kirk: How close will we come to the nearest Klingon outpost if we continue on our present course?
Chekov: Ah, one parsec, sir. Close enough to smell them. [grins broadly]
Spock: That is illogical, Ensign. Odors cannot travel through the vacuum of space.
Chekov: I was making a little joke, sir.
Spock: Extremely little, Ensign.
The working title for this popular/comedic ep was “A Fuzzy Thing Happened to Me…” (LOL)! Having received a Priority One distress call from an outlying space station, the Enterprise arrives to find they’ve been summoned there by a self-important Federation commissioner, Nilz Baris (William Schallert), to protect a shipment of seeds (quadrotriticale) meant to sow wheat on Sherman’s planet. The planet is coveted by the Klingons, who are taking shore leave at the station. Koloth (William Campbell) cites authority to shore leave rights as authorized by the Organian Treaty; this occurred in Errand of Mercy when the Organians prevented a war between the Federation and the Klingon Empire. The Treaty of Organia dictates interactions between the two sides to prevent another chance of war. The trouble arises w/ tribbles- small furry creatures that seem to multiply w/o end. However, their presence reveals both a problem w/ the wheat and a spy on the space station.
Spock: [while holding a tribble] Most curious creature, Captain. Its trilling seems to have a tranquilizing effect on the human nervous system.
Spock: [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]
When McCoy figures out that the tribbles are in a perpetual state of being pregnant, this marks one of the very first instances on American TV of the use of that word. While McCoy is telling the good things about tribbles, Spock takes a jab at him by saying that one good thing about tribbles is that they don’t talk much. William Shatner recalled: “The trouble we had with Tribbles was [to] keep your straight face. It was just a lot of fun.” The scene in which Kirk is buried in an avalanche of tribbles took eight takes to get right. The tribbles were thrown into the hatch by the production crew, but were not sure when to stop b/c they were unable to see the scene. This is why additional tribbles keep falling on Kirk one by one. Shatner looks perplexed (almost breaking the fourth wall for a moment) in that scene.
[Kirk is testing the tribbles’ reaction on several people, starting with the Klingons. The tribbles squeal]
Capt. Kirk: …They don’t like Klingons. [He moves on]
Capt. Kirk: But they do like Vulcans. Well, Mr. Spock, I didn’t know you had it in you.
Spock: Obviously, tribbles are very perceptive creatures, Captain.
To create the one tribble moving on its own, the prop supervisor bought a battery powered toy dog and stripped it down to the mechanical works. Once recovered w/ fur incl. the toy legs, the prop moved on camera along the railing on the Enterprise bridge without wires or external assistance. The toy was so noisy all the dialogue in the scene had to be looped w/ ADR (re-recorded after shooting). The noises that the tribbles make were a combination of dove cooing, screeching owl cries, and air escaping from balloons. Tribbles have made appearances in different versions of Star Trek, incl. Star Trek: Deep Space Nine: Trials and Tribble-ations (1996).
 Sometimes an episode like this is needed to keep the fun flowing… refreshing change from the drama that is prevalent throughout the series. I also love the fighting between Kirk’s crew and the Klingons – that is a barrel of laughs. In fact, there is humor all though this episode – that is the appeal of it.
 Here, the mundane, the banal, is thrust upon him [Kirk]: instead of being allowed to explore the galaxy in the grandest tradition, he’s forced to guard a bunch of wheat.
It’s a farce, Trek style.
 Shatner wears a great air of weary disbelief about everything and he has plenty of great lines… …he shows a real comic touch here and I was rolling with laughter as he stands up to his chest in Tribbles being pelted from above by them while delivering his lines. Nimoy enjoys himself too with lots of “raised eyebrow” moments…
-Excerpts from IMDB reviews