Mutual masturbation, mutual manual stimulation of the genitals between partners, can be a substitute for sexual penetration. Although there may be no connection between coprophilia and sadomasochism , the limited data on the former comes from studies of the latter. No causal relationship is known between masturbation and any form of mental or physical disorder. Reality pornography is a genre of pornography where staged scenes, hentai porn usually shot in cinéma vérité fashion, set up and precede sexual encounters. These actors often play the top roles but this is not always the case, such as with Kristen Bjorn and some Bel Ami models. In some creampie films, both gay and straight, intercourse and internal ejaculation are followed by performers licking up the semen that has dripped from their bodies. Threesome or 3some pornography features one man and two women . Some people masturbate by using machines that simulate intercourse. The two sets of people involved often meet either lesbian milfs randomly or arrange to meet up beforehand over the Internet. Solo pornography recognized with AVN Awards include the All Alone series and All Natural: Glamour Solos. Female masturbation involves the stroking or rubbing of a woman vulva, especially her clitoris, with an index or middle fingers, or both. Lesbian pornography typically features a wider range of appearances and body types than is typical of mainstream pornography. Cum shots typically do not appear in girl-girl scenes and orgasm is normally implied by utterances, cinematic conventions, or body movement. The term is typically used by the cinematographer within the narrative framework of a pornographic film, and since the 1970s has become a leitmotif of the hardcore genre. Production of such films was profitable, and a number of producers specialised in their production. A scene where many women gay twinks have sex with one man is referred to as a reverse gang-bang. His most famous model was Bettie Page, who became the first celebrity of bondage film and photography.