A variant of A2M is ATOM where a performer inserts his penis directly from one recipient anus into a second recipient mouth. BDSM is a variety of erotic practices involving dominance and submission, role-playing, restraint, and other interpersonal dynamics. Interracial pornographic films have experienced an explosion in popularity, becoming one of the fastest-growing and biggest-selling genres. Such films continued to be produced but could only be distributed by underground channels. In pornography, depictions of lesbian sex form a popular subgenre, directed toward a male heterosexual and female homosexual audience. 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. Gloryhole pornography features women performing fellatio on unidentified men through a small hole made in a 3d hentai bathroom divider. Pornographic films present sexual fantasies and usually include erotically stimulating material such as nudity. Matsuo used amateur actresses in his videos, and he usually traveled to their hometowns for the filming. The person receiving anilingus is regarded as the passive partner in the act, and the person performing anilingus is the active partner. It is used, for example, at fertility clinics to stimulate sperm donors. The prostate gland is one of the organs that contributes fluid to semen. In some societies, the terms milf xxx fox, plum, chick, or chicken hardcore gay sex are preferred. A variation on this is to place the gay movies fingers and thumb on the penis as if playing a flute, and then shuttle them back and forth. Pornography may be presented in a variety of media, including books, magazines, postcards, photographs, sculpture, drawing, painting, animation, sound recording, film, video, and video games. Lesbian pornography made for women is usually made by women, and usually features women who identify as lesbian or bisexual. 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.