We all know the best you can do with an acorn (turn it into an oak), but what can we do with a cupule? One answer is: whistle! It is a good skill to learn. If you are ever lost in the woods, you can use it to emit a shrill call for help or to whistle a happy tune so that no one knows you are afraid. In some regions of the world there seems to have been a long tradition of acorn-cap whistling, particularly among Spanish goatherds. In Mexico, too, children are known to use acorns for whistling.