When the final scene in the film was being shot, the crew realized no one had created the tribble that was supposed to appear in the scene. The crew finally resorted to using the furry-looking windsock off the boom microphone, which they pushed up in a box which had the bottom cut out. Actress Grace Lee Whitney moved her fingers inside the windsock to make the "tribble" appear to move.
In the marriage scene between Uhura and Stonn (Lawrence Montaigne), the priestess is played by Arlene Martel, who appeared in "Amok Time" (1967) as T'Pring, Spock's fiancée. Spock rejected her after challenging him and she ended the episode married to Stonn.
Apollo 11 astronauts Neil Armstrong and Buzz Aldrin were both offered roles as Admirals on the Enterprise-M vessel. Both were very interested, but neither space pioneer could be suitable for the shoot into their busy schedules.