Many people are able to whistle, that is, to produce sound by forcing air through their lips which are shaped to create the required turbulence and a resonant chamber (the mouth). A more intense whistle may be created using the fingers to shape the opening - this allows the mouth to relax permitting a much more forceful stream to be blown through. This type of whistle is usually called a wolf-whistle.
Whistling can be varied in pitch to produce music; many performers on the Music Hall and Vaudeville were professional whistlers.
There are also whistled languages.
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