Ben Wa balls, also known asorgasm balls,rin-no-tama,Venus ballsorGeisha balls("vaginaball", "internal-use ball"), are small, marble-sized balls, usually hollow and containing a small weight, that roll around and are used forsexualstimulation by insertion into thevagina. Available in a variety of forms, the balls may be solid or contain clappers or chimes within. Other, larger versions made of plastic encasing lesser balls are calledDuotone balls. They are used by inserting them into the vagina and using thepubococcygeus musclesto hold them in, stimulating movement and/or vibration. Ben Wa balls should not be confused with anal kegel exercisers and prostate stimulators for men: Ben Wa balls sometimes have a retrieval string or attachment of some sort, but they do not have an adequately flared base for safe anal play.