When Lord Krishna plays upon His flute mountains melt and water becomes solid. Hearing the sweet sound of His flute, the trees blossom, cows and calves would become stunned, weeping in ecstasy, embracing Krishna in their hearts. When the gopas hear the sound of the flute they celebrate by playing and wrestling with Krishna.
Lord Caitanya Mahaprabhu explained that when the sound of the flute enters the ears of the gopis, it is like a bird that enters into their ears and make a nest so that no other sound can enter their ears and no other thought can possibly come into their hearts.
– Radhanath Swami