Unlike other Americans who acted in Toho's science fiction films, such as Russ Tamblyn or Rhodes Reason, actor Nick Adams had no contempt for his work and expressed genuine interest in the hard work of the special effects staff and befriended much of the cast. The same year Adams would recount his positive experiences in an article for the Los Angeles Herald-Examiner, "A Kind Word for Those Monster Movies".
The effect of the water seemingly exploding when the flying saucers emerge from the lake was achieved by filling a thermos full of carbon dioxide and exploding it underwater.
Nick Adams is speaking English throughout the film, while the other actors conversed in their native Japanese. Adams was dubbed over into Japanese for the Japanese release. Conversely, when the film was finally released in the US, Adams' voice is the only one not dubbed over. This is similar to how spaghetti westerns were made with the actors speaking in their native tongue, with the latter being dubbed for foreign release.
While this was still the era in which Godzilla films had large budgets and crew, it does mark was the first time a Godzilla film used a noticeable amount of stock footage from previous movies. In this case under 2 minutes culled from MOTHRA and RODAN.
Godzilla's "victory dance" after defeating King Ghidorah on Planet X was based upon the "shê" gag pose, a trademark of the mischievous character Iyami from the manga "Osomatsu-kun," created by famous Japanese cartoonist Fujio Akatsuka. Iyami would go into this pose every time he is surprised, and scream "shê!" This became a famous pose in Japanese popular culture, especially around the production of this film. Actor Yoshio Tsuchiya suggested that Godzilla do the pose too so Toho made the request to effects director Eiji Tsuburaya. He agreed, cleverly incorporating the pose into a "victory dance" for the monster. Tsyburaya though it was so funny that he had Godzilla do it multiple times in the scene instead of just one. While Tsyburaya had no qualms about adding such lighthearted moments, in fact he would often encourage it, director Ishirô Honda vehemently opposed. Honda's son Ryuji recalled that despite his father disliking the decision, there wasn't anything he could do due to studio mandates. Honda also didn't argue with Tsyburaya due to the immense respect he had for him.