Duo Balls: A wonderful invention. For use internally, Duo Balls go way back to ancient China. Each Ball has a heavy ball inside that moves randomly dependent on external stimulus such as walking, jogging, or even swaying backwards and forwards on a crowded train. Use around the home for more person pleasure, or with a partner during oral sex.  Balls are super soft with a Black & White marblized pattern and, of course, internal weights for non stop movement. Strong pull cord with a three inch loopleash makes these Duo Balls easier to keep and clean.