Although this was the first episode to air on NBC, it was actually the sixth episode produced. NBC chose to air this episode first because they felt that it had more action than any of the first 5 episodes and it also featured a monster.
Dr. McCoy's handheld "medical scanners" were actually modified salt and pepper shakers, purchased originally for use in "The Man Trap", in which a character was seen using a salt shaker. They were of Scandinavian design, and on screen were not recognizable as salt shakers; so a few generic salt shakers were borrowed from the studio commissary, and the "futuristic" looking shakers became McCoy's medical instruments.
Uhura's line, "Sometimes I think if I hear the word 'frequency' again I'll cry", is drawn from an incident during filming. As early as it was in the series, Nichelle Nichols was already tiring of the repeated line, "Hailing frequency open, sir"; at one point she turned to Leonard Nimoy and told him, "If I have to say the word 'frequency' one more time, I'll blow up this goddamn panel."
This is the only episode in which McCoy's quarters are shown. A pan and cut along a blank wall allowed two McCoys to appear in the same room. The three cylindrical containers on the shelf in McCoy's room were previously seen on Ben Childress's table in Star Trek: Mudd's Women (1966). These cylindrical containers later appear in the large lighted shelf display area in McCoy's lab.
Dr. Crater states that the buffalo (Bison) of North America had been hunted to extinction. Though they had been nearly hunted to extinction by 1966, it is now unlikely that they will go extinct as they now number around 350,000.
As one of the first episodes of Star Trek ever produced, the production effects had yet to be fully "ironed out", which is evident on the surface of the planet when Kirk and company are calling out "Crewman Green, report!" While the characters are supposed to be outside on an open plain, the way their voices sound makes it very obvious that the actors are calling out on an enclosed indoors stage.
William Shatner has severe problems to this day with persistent ringing in his ears, a condition known as tinnitus. He says it was caused by explosions going off near him during his television work. In both this episode and Star Trek: Arena (1967), explosions occur very close to Shatner. Leonard Nimoy also had tinnitus due to this occurrence, but not as severe as Shatner's.
A unique phaser ricochet sound effect is used when Crater is stunned by a phaser shot, the only time this effect is ever used in the original series. Alfred Ryder's voice then slows down, representing the stun effect.
One aspect of the first season episodes is that the crew are not just walking in the corridors; they are often engaged in maintenance work, checking out equipment in the corridors and so on. This is evident in this episode and Star Trek: Charlie X (1966), especially. Minor crew members also carried on casual conversations and a feeling of the ship as a real community was created, as when Uhura asks Bobby to fix her rattling door or when two crewmen admire Janice Rand. These details about everyday life on a starship largely faded away as the series progressed.
During the production, Marc Daniels introduced a system in which cast who were not needed on a shoot would go to a "cast table" area and sit with the other actors to practice upcoming scenes, rather than being allowed to return to their dressing rooms. This sped up the filming process, and the producers felt that it also improved the quality of the performances. The cast table system continued to be used throughout the production of The Original Series, even when Daniels was not directing the episode in question.
This was the first episode that David Gerrold viewed. Watching it upon its first airing, Gerrold was thrilled by what he saw, later reminiscing, "I watched it eagerly. I was amazed that something this imaginative had made it to television."
The first draft of this episode's script was completed on 13 June 1966, with the final draft being completed three days later. George Clayton Johnson recalled that story editor John D.F. Black's only major objection to his first draft was that the M-113 creature did not arrive aboard the Enterprise until the third act. Black argued that the crew had to be put in jeopardy sooner, and so Johnson revised the script accordingly.
In the original script, the moral dilemma of killing 'the last of its kind' had been more pronounced, with the creature, disguised as McCoy, trying to reason with the crew. Also in that version, Professor Crater lives in the end, mourning the loss of the creature. Gene Roddenberry's rewrite for the final draft toned down the emotional aspects of the McCoy relationship in favor of a more straightforward plot, as a cornered animal, the salt creature panics and actually kills it's longtime companion; Professor Crater.
Sulu's botanical collection was much more lavish in George Clayton Johnson's original script, including a plant resembling the face of a Chinese dog, etc. This was eliminated for budgetary reasons, Beauregard remaining the only moving "exotic plant".
It was Gene Roddenberry's idea to have the creature, in its illusory form, speak Swahili to Uhura. Kellam de Forest supplied him with the translation. In English, the illusory crewman says "How are you, friend. I think of you, beautiful lady. You should never know loneliness."
As the first episode actually telecast, the opening credits are slightly different from most other first season shows. Gene Roddenberry has "created by" credits and there is no "starring" before William Shatner's name. This version of the credits was used only once more, in Star Trek: Charlie X (1966).
In one of the red alert scenes on an Enterprise corridor, the crewmen are wearing turtleneck uniforms. It is a recycled (originally unused) shot from Star Trek: Where No Man Has Gone Before (1966). (It can be seen at the beginning of Act One, in the original, pre-broadcast version of the second pilot.)
The very first Enterprise crew members whom the television audience saw in this premiere episode were Spock, Uhura, and Leslie, sitting in the command module on the bridge (which is, in fact, a recycled shot from Star Trek: The Naked Time (1966)).
In early episodes like this one, there are up and down indicators that light up outside the turbolifts. Although they are seen in subsequent episodes, only in the earliest ones do they actually light up to indicate direction of travel. Elevator indicator lights later show up in engineering above one of the consoles.
The bridge sound effects still retain sounds from the two pilots. By the time Gene Roddenberry left as producer, those original sounds were not heard again, with the brief exceptions of being heard while on the bridges of the Exeter and the Lexington. The DVD releases, however, have overlaid these older sound effects in every episode. They are presented as "rear channel" sounds which gives the episodes a "surround sound" effect.
When Nancy Crater first walks into the dig headquarters, Nichelle Nichols' singing from Star Trek: Charlie X (1966) is briefly dubbed in. Curiously, Nancy's mouth does not appear to move as she is singing.
The shot of the computer monitor in sickbay, then in McCoy's quarters is the same shot, is recycled from Star Trek: The Corbomite Maneuver (1966) (with the close-ups of Kirk and Spock matted in during post-production).
Kirk's run down the corridor to the sickbay is recycled footage from Star Trek: The Naked Time (1966) as is a reaction shot of Kirk when Spock is telling him about the Borgia plant on the sickbay video display interface.
The statue near the entrance of the Crater home can later be seen in Spock's quarters in Star Trek: Amok Time (1967) and subsequent episodes. In a blooper shot, a man's arm can be seen putting a cigar into the statue's mouth.
Grace Lee Whitney considers the arboretum scene of Rand and Sulu as one of her favourite scenes of the series. She recalled that shooting the scene was quite funny, and the entire cast and crew were in a lighthearted atmosphere. Some crude jokes were told in connection with Beauregard and her, and even the puppeteer below the table (Bob Baker) tried to reach for her short skirt with the puppet. Whitney later described this episode as "filled with plenty of horrific and suspenseful moments. It was a great debut episode for the series."
The episode made an impression on future Star Trek: Enterprise (2001) staff writer Chris Black, who was in kindergarten at the time he saw the installment. "I remember [...] seeing the salt vampire,' the M-113 creature, and running out of the room in terror".
In Leonard Nimoy: Star Trek Memories (1983), Leonard Nimoy mentioned the fact that NBC chose to air this episode first, since (at least to the network) it was "proper" science fiction with a "proper" alien menace. Nimoy also stated that of the episodes the cast and crew had already completed, this was their least favourite.
When it came for the set to be redressed to appear as the ship's sickbay, Marc Daniels made the decision that Vulcans should have green blood for the scene in which Spock bleeds, but Gene Roddenberry disliked it and attempted to have it corrected in post-production.
During the writing process, there was some consideration by the productions given to what the creature would look like. Robert H. Justman suggested to Gene Roddenberry that it could be some sort of "terrifying, young lady" with a similar appearance to the green skinned Orion slave girl seen in Star Trek: The Cage (1986), but blue skinned and with orange hair. Roddenberry thought that the idea was good, but said that they had to keep to it being an "animal" as that was what NBC had already agreed. George Clayton Johnson had envisaged the creature as a refugee with "ashen skin" wearing "gunnysack clothing". Marc Daniels had some apprehension about using a monster of the week format, asking "Do you go for cheap thrills or a more intelligent approach?", adding that they decided to "treat everything as if it were real" in order to ensure that the audience bought into it.
The head of the creature costume were first sculpted in clay and then covered in a plaster cast. Once the cast was removed, liquid latex was applied to create a flexible single piece mask. It was then painted, and Wah Chang added a white wig and attached glass lenses to the mask for eyes. Once Sandra Lee Gimpel was wearing the mask, cuts were made into the wrinkles in order to offer the actress some limited vision while wearing it. A pair of gloves were modified by Chang to give the fingers the appearance of tentacles with suction cups. William Ware Theiss created the rest of the costume out of a fur bodysuit.