[Kamog]

I remember watching that Original Series episode where they encounter the Romulan ship, and it looks like a Klingon ship.

"That's a Klingon ship!"
"But it couldn't be, not in this area."
"Intelligence reports Romulans now using Klingon design."

My friend and I joked about this. We thought this is what happened when they were filming the episode:
...
Gene Roddenberry: "OK, now let's show the Romulan ship on the main screen, approaching the Enterprise."

*William Shatner accidentally knocks the model Romulan ship onto the floor, smashing it.*

William Shatner: "Ooops!"

Gene Roddenberry: "Hey, that's our ONLY Romulan ship model! What are we going to do?!"

Leonard Nimoy: "Um, we have this Klingon ship model. Let's just use that and say that the Romulans got the design in a trade agreement with the Klingons."

Gene Roddenberry: "All right, I guess we have no choice, we'll do that."

*William Shatner accidentally drops the Klingon model ship and wrecks it*

William Shatner: "Ooops!"

Gene Roddenberry: "Oh, no! NOW what do we do?"
...
So in the episode.... "Sir, the Romulans are now using Federation design!..."