TREKCORE > TOS > EPISODES > THE ENEMY WITHIN > Behind the Scenes

	First instance of a double of Captain Kirk. Others would appear in "What Are Little Girls Made Of?", "Mirror, Mirror", "Whom Gods Destroy", and "Star Trek VI: The Undiscovered Country".
	First instance of the Vulcan Neck Pinch. The script originally called for Mr. Spock to knock the Evil Kirk out with the butt of his phaser, but Leonard Nimoy objected, saying that Mr. Spock "would probably have a Vulcan way of rendering someone unconscious".
	First instance of Dr. McCoy's "He's dead, Jim" line.
	Kirk's "Captain's Tunic" was introduced here to help differentiate between the Good Kirk and the Evil Kirk.
	Edward Madden, who plays Geological Technician Fisher, had previously played the unnamed Enterprise geologist (perhaps Fisher as well) in "The Cage".
	Even though the transporter is unusable, no one considers sending a shuttlecraft down to the planet to rescue the landing party, but that can be chalked up to the fact that the producers weren't entirely sure of the compliments of the Enterprise by this point in the series.