One of the most famous and ubiquitous pieces of Star Trek canon was originally something far less elegant.
When it comes to Vulcan customs, the famed Vulcan nerve pinch is second in fame only to the combination of the Vulcan salute and the words "Live Long and prosper" (OK, and maybe the mind meld, too). It's been used throughout the Star Trek universe for decades, and it's been referenced and lampooned countless times throughout pop culture. It's hard to imagine a Star Trek universe that didn't contain the Vulcan nerve pinch, but the moment when it was first used was originally written as a simple punch to the face.
In the fifth episode of the first season of Star Trek: The Original Series, "The Enemy Within," Captain Kirk is split into two people -- a good Kirk and an evil Kirk -- due to a transporter mafunction. Spock is tasked with taking out the evil incarnation of Kirk, and the script called for him to simply knock evil Kirk out with a punch. Nimoy objected to the punch idea, believing that Vulcans would have a more sophisticated, less violent way of incapacitating their opponents.
So, instead of belting Shatner across the face, Nimoy pitched the idea that Vulcans could emanate energy from their fingertips, and if they applied that energy to a particular set of nerves on the human body, they could use it to knock someone unconscious. They tried it Nimoy's way on set, it worked out, and from then on the gesture was referred to as FSNP (Famous Spock Nerve Pinch) whenever it was called for in Star Trek scripts.
So we have Nimoy to thank not only for the Vulcan salute, but also for the Vulcan nerve pinch, two gestures it's hard to picture the character of Spock without.
And check out these other little-known sci-fi facts: