"If it is not wholly visionary at every juncture, it is at least dependably — even exhilaratingly — bizarre. Its strangeness, which borders cheerfully on the ridiculous, is its most enjoyable feature. The movie itself has many of the qualities of its chief character, who is obsessive, exciting, scary, wildly energetic, and a very odd bird indeed. Actually his leanings are more to the ape-like than the birdlike, and to call them leanings is to put it very mildly. … The movie, part joke and part nightmare, is the story of a man who experiments with hallucinogenic substances, searching for what he calls his unborn soul and longing to re-experience the birth of man. In the course of this adventure, he turns into an ape and scares the daylights out of everyone around him. Really, that's all you need to know. … The film is in fine shape as long as it revels in its own craziness, making no claims on the viewer's reason. But when it asks you to believe that what you're watching may really be happening, and to wonder what it means, it is asking far too much. By the time it begins straining for an ending both happy and hysterical, it has lost all of its mystery, and most of its magic."