Works in this genre may be considered adult for any number of reasons. A study of 164 males in Finland from two SM clubs found that 18.2% had engaged in coprophilia; 3% as a sadist, 6.1% as a masochist, and 9.1% as both. 18% of heterosexuals and 17% of homosexuals in the study pool had tried coprophilia, showing no statistically significant difference between heterosexuals and homosexuals. The glans itself may widen and lengthen as the stimulation continues, becoming slightly darker in colour, while the gliding action of the foreskin reduces friction. It has since become popular enough with couples to be discussed during an episode of Sex and the City. Group sex most commonly takes place in a private sex party or semi-public swinger gathering, horny milfs but may also take place at massage parlors or brothels or, in some jurisdictions, at purpose-built locations such as sex clubs. Some aspects of the research community distinguish between female ejaculation and what is colloquially known as squirting or gushing. Bondage pornography specializes in the depiction of sexual bondage or BDSM activities as photographs, stories, movies, or 3d hentai drawings. Sadomasochism refers to the aspects of BDSM surrounding the exchange of physical or emotional pain. People may experience pleasure from anal sex by stimulation of the anal nerve endings, and orgasm may be achieved through anal penetration – by indirect stimulation of the prostate in men, indirect clitoral/G-spot stimulation in women, and associated sensory nerves . Solo pornography recognized with AVN Awards include the All Alone series and All Natural: Glamour Solos. Breeding gay fuck is sometimes followed by felching naked celebrities , which involves sucking the semen from the partner anus. Erotic spankings are commonly combined with other forms of sexual foreplay. The term BDSM dates back to 1969; however, the origin of the term BDSM is unclear and is believed to have been formed either from joining the term B&D with S&M , or as a compound initialism from B&D, D&S , and S&M.