10 Star Trek Facts You Probably Didn't Know
3. The Vulcan Nerve Pinch Was Improvised
The Enemy Within is an episode of TOS in which a transporter accident causes Captain Kirk to be split into a good and evil version of himself. It also was the first episode to show the now iconic Vulcan nerve pinch: a sharp grasp to the neck that causes the recipient to fall unconscious. Now an iconic part of Star Trek lore, it wasn't originally a part of the script.
Initially, Spock was meant to incapacitate the captain through force. Leonard Nimoy felt this seemed out of character. Vulcans were meant to be logical and were supposed to dislike violence. To physically knock someone out seemed too brutish for the alien. Nimoy suggested the nerve pinch, instead.
It is said that he and William Shatner practiced the idea and when it was time to film the scene they showed off Kirk dramatically collapsing from the well-executed pinch. Director Leon Penn loved the idea. It was used in the episode and has since shown up in many episodes throughout the franchise.