Sentence:  He is especially fascinated by the "chacha", the percussion instrument that sets the basic rolling rhythmic foundation of the <WSD>beguine</WSD> and propels the dancers, writing that “the tempo is set by a shiny tin container filled with pebbles....″ 
Meaning of the word marked with <WSD> tags:  A ballroom dance, similar to a slow rumba, originally from French West Indies and popularized abroad largely through the song "Begin the Beguine"; the music for the dance.