"The Manster (双頭の殺人鬼?, Sôtô no Satsujinki) is a tokusatsu 1959 horror film, a co-production between the US and Japan, starring Peter Dyneley. The film was notable for its creative use of special effects. The film is also known as The Split in the United Kingdom, Doktor Satan in Greece, and The Two-Headed Monster.
The plot concerns an American reporter in Japan who is sent to interview an eccentric Japanese scientist working on bizarre experiments in his mountain laboratory. When the doctor realizes that the hapless correspondent is the perfect subject for his next experiment, he drugs the unfortunate man and injects him with a serum that gradually transforms him into a hideous, two-headed monster.
Recently, film critic Richard Scheib gave the film a qualified positive review, writing, 'This American-Japanese co-production is an interestingly obscure film, one whose reputation as a B movie has preceded its actual availability on video or tv. It is of course a venture into the schlock movie theme of the two-headed transplant. But The Manster is one entry that, when seen, proves a whole lot more entertaining than other variants on the theme such as the terrible The Incredible 2-Headed Transplant (1971) and the deliberately silly The Thing with Two Heads (1972).'
Sam Raimi's Army of Darkness (1992) pays homage to this film. When Ash has swallowed one of his little dopplegangers, he grows an eye on his right shoulder, which results in him splitting into two beings; Good Ash and Evil Ash. In this film, the reporter is injected with a serum and later develops an eye, which grows into a head, resulting in him splitting into a good being and an evil one. This film was originally released in the US on double feature with George Franju's Eyes Without a Face (1960)."