grass whistle

press a blade of grass flush between the palms of your hands, hold the heels of your hands to your lips, and blow, producing a whistle.

Willie learned this at some point in his childhood, though he does not exactly recall when or from whom. The grass whistle is a widespread piece of childhood folklore, being a simple, yet fun object for kids to make noise with. Children tend to make entertaining toys out of their surroundings, and they learn it from each other, just playing outside, as children do.