Balls or Kegal exercise balls, are small, marble-sized metal, silicone or plastic 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. They are used by inserting them into the vagina or anus and using muscles to hold them in, and movement to stimulate and vibrate. Balls can be worn inside the vagina for extended periods of time. The internal rolling is claimed to enhance orgasms.