Castanets are a percussion instrument consisting of a pair of concave shells joined by a string. They are used in Spanish, Kalo, Moorish, Ottoman, Italian, Sephardic, Swiss, and Portuguese music. To play them, one pair is held in each hand with the string hooked over the thumb and shells resting in the palm. When the hands are clicked together they produce rhythmic clicks or rattles. Originally made from chestnuts, castanets were used by ancient Greeks and Egyptians. Famous castanet players include Carmen Amaya, Lola Flores, and Alex Acuña.