The red thing from our Minimal Whistle cursor is an instrument that produces sound from a stream of gas, most commonly air. It may be mouth-operated or powered by air pressure, steam, or other means. Whistles are different in size, from a small slide whistle or nose flute type to a big multi-piped church organ. By the way, During World War I, officers of the British Army and United States Army used whistles to communicate with troops, command charges, and warn when artillery pieces were going to fire.