When tree sap is running, cut off straight, smooth piece from willow branch about 4″ (10 cm.) long and 3/4″ (1.9 cm.) in diameter.
Using sharp pocketknife and whittling away from you, cut slanting slice off thinner end. Square off point (Fig. 1).
Turn willow piece over and notch through bark 1/2″ (1.25 cm.) from mouthpiece end (Fig. 1).
Make circle cut just through bark 3″ (7.5 cm.) from mouthpiece end (Fig. 1). Now gently tap bark (mouthpiece end) on all sides with knife handle to loosen bark without cracking it. Bark should pull off in one piece (Fig. 2) because sap has made inside of bark slippery.
With bark cylinder removed, lengthen notch in wood to 1″ (2.5 cm.) and deepen it slightly (Fig. 3).
To make air passage, shave thin, flat slice from end of notch to end of mouthpiece (Fig. 3).
Completely wet both willow pieces before slipping bark cylinder back onto whistle. Move bark cylinder back and forth to change whistle’s tone.