The Delta Triangle is a transparently obviously based on the Bermuda Triangle - a mysterious region where ships supposedly vanish for no apparent reason. Only in the best Space is an Ocean tradition, they don't even bother dealing with the fact that on a planet's surface, a triangular zone makes sense, whereas in space it makes no sense at all - a zone should be a volume, not a plane figure.

It's also rather odd that Kirk doesn't figure out Spock's trick to get information out of the Klingons before Spock explains it. (In fact, in the episode, both Kirk and McCoy worry that something is psychologically wrong with Spock, and question him about it.) Watching the episode, as soon as I saw Spock touch the Klingons I knew what he was up to. You'd think Kirk would have an even better idea of what Spock was doing, rather than be mystified.

Transcript

1
Captain's log, Stardate 5267.2. The Delta Triangle, where ships mysteriously vanish.
Spock: A triangle is two-dimensional. In space we could avoid it simply by—
Sulu: Entering the triangle!
2
Caption: Trapped in a ship graveyard with Klingons!
Kirk: Fire!
Kor: Fire!
Other ship: Oh, no you don't...
3
Devna: We are trapped in a pocket universe where time passes slowly. A century means nothing to us.
Xerius: Any violence is punishable by a century of confinement!
Kirk: Screw that, we're getting out of here.
4
Spock: {hugging Kor} Let's join our ships to give us the power to escape this place.
Kor: Yes. We won't sabotage the Enterprise and blow you up as soon as we're free.
Spock: Good, good.
5
Kirk: What's with the touchy-feely with Kor? Mudd's love crystals again?
Spock: The Vulcan mind touch. They plan to doublecross and destroy us.
Kirk: A Klingon? Wow, I never would have guessed that, Spock!
6
Sulu: It worked! Were free!
McCoy: Have we psychologically destroyed another society, by disproving their belief that they are trapped?
Kirk: Ehh. They're still trapped. We'll never know!