Shepherd's whistle
They are also produced commercially. Simple whistles may cost less than 1 USD in bulk; expensive ones may be quite ornate. They are commonly made of plastic, aluminum, stainless steel, silver, brass, titanium, Corian, jade, buffalo horn and other materials.
Whistle register
The whistle register (also called the flute register or whistle tone) is the highest register of the human voice, lying above the modal register and falsetto register. This register has a specific physiological production that is different from the other registers, and is so called because the timbre of the notes that are produced from this register is similar to that of a whistle.