There are two different US versions of this film: One is the American International Pictures print with the original atmospheric music score (complete with classical music pieces), and during the climactic fight between Popoca and the Human Robot, Popoca had a scary, menacing voice (ie. groaning and roaring). Another is the 1964 rerelease by Young Horror Club of America, with a completely redone (and loopy) music score, somewhat different title cards, and the voice of Popoca (in said climactic fight) was replaced with a faint high-pitched voice (which sounded more like he was yawning). This latter version was seen in the public domain. Both versions had the exact same dubbing done for US producer K. Gordon Murray by Manuel San Fernando (intended for AIP's version).