In the script, McCoy and Scott have a scene in which they explain to Kirk how they figured out which computer bank Spock tampered with to lock the ship on course. They took perspiration readings on all banks, and since Spock's sweat has copper in it, traces of copper were found. This scene isn't shown.
When Number One and Yeoman J.M. Colt transport to the planet, Vina states that Capt. Pike would be better reproducing with a computer than Number One. Majel Barrett provided the standard Federation computer voice throughout the various Star Trek series.
This is the only episode of any Star Trek series which uses a captain's log to recap the events of the previous episode in a story arc. All others use a more traditional "previously on..."-type of recap.
The original pilot The Cage (1966) was directed by Robert Butler and the new framework story by Marc Daniels. Since The Menagerie: Part I (1966) consists mostly of framework and Part II is primarily made up out of 'The Cage,' Daniels received directing credits for the first part and Butler for the second. The same applies to the crew listed during the end credits: part 1 lists the regular series crew, part 2 those of the pilot.
The Talosian "Keeper" alien was actually played by a woman - Meg Wyllie, as were all Talosians. The voice was dubbed by Malachi Throne, who portrays Commodore Jose Mendez. In order to differentiate the 'Talosians' voice from the Commodores, Throne's voice as the Talosian was slightly sped up.