If you can find it, this documentary is a lot of fun: Pucker Up - The Fine Art of Whistling There is a short, but great segment where this is demonstrated w

If you can find it, this documentary is a lot of fun: Pucker Up - The Fine Art of Whistling There is a short, but great segment where this is demonstrated with two men whistling across mountain tops to communicate. The film is filled with gems like one guy explaining as a compulsive whistler he got in trouble once for whistling a tune at a funeral.