Snake charmers in India keep cobras or other very poisonous snakes in a sack. To entertain people, they play the flute, and the snake writhes out of the sack and dances to the music. But, since the snake has no ears it can't actually hear the music! In fact it weaves its head about as it watches the movements of the flute, or feels the vibration of the charmer's tapping feet.