If I recall, and I'm going from memory here, the director of Manos had a camera that could hold 10 minutes of film at a time. Either he didn't realize he could use less than the full reel for a scene, or didn't want to waste film, or didn't know how to edit--but he tended to just film the full can once he started. That's why you get scenes of 10 minutes of a car driving (instead of, you know, actual plot), throughout the film.