The sound of cracking walnuts.

The sound of the castanets is produced by the collision of two shell-shaped pieces of ebony or mahogany, like the sound of smashing walnuts.

The castanets were mainly used to accompany singing and dancing, and were later also used in European art music. Initially, two pieces of wood were tied to the thumb and middle finger respectively, and later they were changed to be played in the palm of the hand.