The reverse of this, gay cock in which nude women interact with clothed men, is called Clothed male, naked female . Group sex pornography features at least two men and two women , usually more, who all perform sex acts on each other. Use of the agreed safeword is seen by some as an explicit withdrawal of consent. These scenes may involve the female actor calling for the shot to be directed at some specific part of her body. Films with risqué content commenced to be produced soon after the invention of the motion picture in the 1880s. Both forms of pornography generally contains nudity. Multiple men and women Bisexual pornography features one woman and two men who all perform sex acts on each other. It is used, for example, at fertility clinics to stimulate sperm donors. Bukkake pornography involves a performer, usually female, onto whom several men or women ejaculate, usually on the face. For circumcised males, on whom the glans is mostly or completely uncovered, this technique creates more direct contact between the hand and the glans. Pornography in Japan is large and intertwined business of adult entertainment with unique characteristics that readily distinguish it from western pornography. The existence of such content in commercially available pornography gay hentai is widely considered an urban legend. As a result, little in history was documented to give an accurate description of how female homosexuality is expressed. It is typically animated milf fuck pornography, as the legal age to be featured in a pornographic film in Japan is 18. The name is a reference to gonzo journalism, in which the reporter is part of the event taking place. Since the 1980s, many practitioners and organizations have adopted the motto safe, sane and consensual, commonly abbreviated as SSC, which means that everything is based on safe activities, that all participants be of sufficiently sound/sane mind to consent, and that all participants do consent. Lying face down on a comfortable surface such as a mattress or pillow, the penis can be rubbed against it.