For other scenes, particularly in established relationships, a safeword may be agreed to signify a warning rather than explicit withdrawal of consent; and a few choose not to use a safeword at all. First found in softcore movies and erotic thrillers, depictions of lesbianism entered mainstream cinema in the 1980s. A female dominant in a master/slave relationship is often termed a Mistress, not to be confused with the colloquial usage of mistress as a kept sexual partner without a similarly formalized power relationship. Actors are mostly amateur; any well-known actors in bisexual porn tend to be from the gay pornography industry. Such films continued to be produced but could only be distributed by underground channels. The effect is to give the viewer the sense that they are experiencing the sex acts that they are watching, as opposed to simply watching others as a voyeur. 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. Amateur porn has been called one of the most profitable and long-lasting genres of pornography. However the genre remains a very small proportion of the pornographic DVD market; for example at porn retailer anime hentai HotMovies. When he is in position the cover is momsex closed. The nipples are erogenous zones, and vigorous stimulation of them during masturbation usually causes the penis to become erect more quickly than it would otherwise. While most tentacle erotica is animated, there are also a few live-action movies. Internal ejaculations, followed by images of semen dripping from the anus, are sometimes depicted in bareback gay pornography, where they are referred to by the term breeding or the reverse money shot. Unlike erotic films, pornographic films contain explicit sexuality and do not claim any artistic merit. It is sometimes described as a sexual fantasy, by women or men, depicting an exhibitionist or physique worship scenario. Interracial pornographic films have experienced an explosion in popularity, becoming one of the fastest-growing gay twinks and biggest-selling genres.