In a magazine article, the special effects department admitted that the "mutant" costume originally had legs that matched the upper body. They had so much trouble making the legs look and work properly they were forced by studio deadline to have the mutant wear a pair of trousers. Movie posters show the mutant as it was supposed to appear.
With the newfound popularity of 20th Century Fox's Cinemascope and other widescreen processes in the mid-1950s, Universal Pictures commenced to develop its own widescreen technology (which would eventually be known as Technirama). As Technirama would not be perfected until 1956, in the interim approximately 50 Universal films released between 1955 and 1957 (including Regreso a la Tierra (1955)) would be shot at full-frame (1.37:1) but carefully composed and photographed in such a way to allow theaters to comfortably exhibit these films at 2:1 (with matting at the top and bottom of the projected image to produce a widescreen effect). Essentially, the same print could be sent to any theater allowing it the option of projecting either a full-frame presentation (in older theaters) or a cropped presentation (for those theaters that had been recently renovated for widescreen exhibition).
The Earth miniature used in the effects shots was also used to make the 1950's-1980's "Earth in Space" Universal Pictures fanfare opening.
A large device, shaped a bit like a desk, with a coiled neon tube in the center, is visible at the Ryberg Electronics laboratory. The prop was also used in the laboratories of Universal Pictures' Frankenstein films of the 1940s.
According to several sources, it took 2 years altogether to complete the special effects - and were very expensive for the time.