We had a high-school English teacher in the early '80s who showed movies instead of teaching every chance he got. The most stultifying, to a teenage audience, anyway, was this 18-minute "documentary" that followed a tumbleweed as it rolled around the desert and into a city. The thing was nominated for the first-ever "short documentary" Oscar. It was the writer's "first and only" film; he almost immediately switched to a career in municipal bonds. It's particularly suited to RiffTrax, as there's no narration whatsoever, and is a sterling example of the '50s art-film movement.