"The Naked Time" is one of the most iconic Star Trek episodes, and for good reasons. Not only did this season-one episode give us George Takei with a rapier fencing across the Enterprise — which started a lifelong love of fencing for the actor — but it was one of our first explorations into the emotional vulnerabilities of the characters.

One of the most crucial scenes has Spock, infected by the virus that suppresses inhibitions, hiding away in an isolated room and desperately trying to cling to Vulcan logic and repression while his human emotions come to the forefront. He attempts to recite mathematical formulas to keep control but breaks down sobbing over his love for his mother and the conflict between his Vulcan and human sides.

It's one of the first chances we have to see the softer side of this unflappable character, but it almost didn't happen.

According to Leonard Nimoy in his autobiography I Am Spock, the scene was supposed to be much more comical. Originally, Spock was supposed to break into tears after a crewman, who had been seen in the episode painting on the walls of the Enterprise after being infected himself, passed by and painted a mustache on Spock. It was a sight gag, and Nimoy felt that it wasn't the significant scene that Spock deserved. 

"It was a funny scene, theatrical and inventive," Nimoy wrote. "But it disturbed me greatly. It...contradicted everything I knew about him." Nimoy felt that with Vulcans and Spock especially valuing dignity, he would never have cried in front of another crewman. "He would maintain control at all costs, and not let down his barriers until he had found a private place."

"It's about emotion versus logic, love versus mathematics, grief versus pi-r-squared," Nimoy said. He convinced John D.F. Black, the writer for the episode, to create the quieter, heavier scene that we see in the final cut.

However, there was one more hurdle — production. Star Trek didn't always have the biggest budget, so going into overtime was out of the question. "Come 6:18 P.M., we had to pull the plug and get off the set, whether the scene was filmed or not —  tomorrow's schedule didn't allow for us to come back and finish it! We have just enough time for one take — so it had to go perfectly!"

So Nimoy did his one take, and what we see onscreen is exactly that. The more emotional scene didn't just fit Nimoy's perception of the character better, it made Spock a household name. Nimoy goes on to note that before the episode aired, he got forty or fifty fan letters. And after "The Naked Time" aired, "the fan mail started arriving in large laundry bags, each containing hundreds of letters."