Noun
(used in the plural) a percussion instrument consisting of a pair of hollow pieces of wood or bone (usually held between the thumb and fingers) that are made to click together (as by Spanish dancers) in rhythm with the dance
Source: WordNetThere was such idiot minstrelsy in rain, So many clappers going without bells, That these bethous compose a heavenly gong. One voice repeating, one tireless chorister, The phrases of a single phrase, ke-ke, A single text, granite monotony. Wallace Stevens
Laws without penalties are like bells without clappers. Czech Proverb