Ben Wa balls, also known as Burmese bells or Geisha balls (In Chinese language|Chinese, Ben Wa balls are called 阴道球 -Pinyin:yīndàoqiú, vagina ball- or 内用球 -Pinyin:nèiyòngqiú, internal-use ball-) are small, marble-sized metal balls, usually hollow and containing a small weight that rolls around—used for sexual stimulation (by insertion into the vagina or anus). Some may also be solid, or contain clappers or chimes within; other larger versions made of plastic encasing lesser balls are called Duotone balls. Reportedly, there is also a pair consisting of one containing a drop of mercury and the other, a tiny vibrating metal tongue, giving a uniquely erotic sensation even at the slightest movement of hips or legs (Sex in History, Reay Tannahill). They are used by inserting them into the vagina