The testicles (or testes; common term: balls), are the principal male organ of reproduction in mammals. They belong to the male genitals. The testicles vary in size and produce sperm that is capable of impregnating a female to create a new being. Most males have two testicles covered by the scrotum, which hangs behind the penis in a standing male.
In certain spanking positions, the testicles and scrotum are presented with the naked buttocks. A skillful spanker knows how to play with the testicles without causing any medical harm. Testes that hang long sway in a pendulous manner. Some spanking players prefer to shield the testicles with a thong or jock strap like a baseball player protects his testicles from a line drive.