Eggs also known as Burmese bells or Geisha balls re 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)giving a uniquely erotic sensation even at the slightest movement of hips or legs. Some may also be solid, or contain clappers or chimes within; other larger versions made of plastic encasing lesser balls are called Duotone balls. They are used by inserting them into the vagina or anus and using muscles to hold them in, and movement to stimulate and vibrate.