Pretty bad, even for a Mexican horror film. Boris Karloff plays a scientist trying to keep a mysterious life form alive by feeding it a brain chemical released by humans when they're terrified. A promising idea, but a woefully put together patchwork of a film. Jack Hill wrote the screenplay and directed Karloff's scenes and they're spliced together with scenes shot in Mexico. Hill's direction of Karloff is pretty bland stuff and the Mexican scenes hold no interest at all, certainly not the few decidedly out of place shots of women being tortured. Isela Vega (electrifying in Peckinpah's "...Alfredo Garcia") appears as "Helga" and shows absolutely zero charisma. This is one US/Mexican tapestry that's shy of quite a few threads.