A variant of this is known as ATOM or ATOGM where the insertive partner removes his penis from one recipient anus and inserts it into a second recipient mouth. Spanking or whipping pornography involves spanking or whipping, generally of the buttocks, with the hand or with other objects such as belts, switches, paddles, brushes, or whips. Masturbation has been depicted in art since prehistoric times and is mentioned and discussed in very early writings. Babysitter pornography hentai movies features usually teenage girls being exploited and having taboo sex with older, male employers. Initially, few animation studios in the United States attempted to produce animation for adult audiences, but later examples of animation produced for adults would gain mainstream attention and success. Simultaneous penetration of the mouth and either the vagina or anus. Mammary intercourse is said by Alex Comfort to produce mutual orgasm in women with sensitive breasts , and it was one of the nine substitute exercises for penetrative sexual activities, as detailed in the Paradis Charnels of 1903. Many men who like trans partners of any variety, known as tranny chasers, do not necessarily identify as gay themselves. Within a BDSM or D/s context, facesitting can be an especially intense form of erotic humiliation. The term is a slang word that milf fuck originated in the gay community and comes from the equestrian term bareback, which refers to the practice of riding a horse without a saddle. The terms can be complimentary gay bear porn or pejorative. The sub-genres usually conform to certain conventions, and each may appeal to a particular audience. This may relate to fetishes such as voyeurism or cuckolding. Group sex is sexual behavior involving more than two participants. The first film was released in 1980 starring Kay Parker. Related genres include: Amateur pornography originally referred only to pornography produced by amateurs but now also includes professionally made pornography designed to appear as if it were amateur.