It's hard to believe anything so small and simple could be so loud and educational!
I learned about this amazing device from Mrs. Wilma Moore. Her husband runs a science club where he teaches at the First Nations Reserve in Northern Saskatchewan, Canada. She said that hunters actually use them when calling in moose.
Aside from the shear fun of it, the moose call demonstrates the concept that makes acoustic stringed instruments (violin, guitar, cello, banjo) as loud as they are. But don't expect to carry a tune on it. In the more about section you can read about what a sound board* is and how it amplifies sound.
*Violin, guitar, and piano strings press down on a bridge which conducts their vibration to a large, thin piece of wood called the soundboard.