Crafted from seasoned wood with two drum heads made from goatskin or synthetic membrane, the Damru produces its characteristic sound through a swinging bead or knot tied to its waist by a cotton cord. When the instrument is rotated by the wrist in a rhythmic back-and-forth motion, the bead strikes both drum heads alternately â producing a rapid, hypnotic "da-da-da-dum" rhythm that has echoed through temples, ashrams and spiritual gatherings for thousands of years.