Going back at least as far as the Christy twins in the 1970s, depictions of incest and particularly naked milf incest between twins has been a feature of gay pornography. Emetophilia pornography involving vomiting and gagging. The first pegging scene appears to have been in the non-pornographic 1970 film Myra Breckinridge, based on the novel of the same name by Gore Vidal, although it was not explicit. Men and women may masturbate until they are close to orgasm, stop for a while to reduce excitement, and then resume masturbating. Examples include the Girls Gone Wild and Girls Who Like Girls Series. Entacle erotica describes a type of pornography most commonly found in Japan which integrates traditional pornography with elements of bestiality and a fantasy, horror, or science-fiction theme. Group sex is gay movies sexual behavior involving more than two participants. The concept of lesbian, to differentiate women with a shared sexual orientation, is a 20th-century construct. Ethnic pornography is a genre of pornography that features performers of specific ethnic groups, or depictions of interracial sexual activity. The term Asiaphile is sometimes used to describe the same phenomenon as is yellow fever . A pearl necklace is a slang term referring to a sexual act in which a man ejaculates semen on or near the neck, chest, or breast of another person. Transsexual pornography features transwomen performers, who typically have male genitalia and augmented female breasts . The padding may also muffle noises from the outside, causing a relaxation effect and heightening their other senses. Unlike erotic films, pornographic films contain explicit sexuality and do not claim any artistic merit. Especially popular in post-World War 2 Japanese culture. 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. Facial cum shots are currently lesbian hentai regularly portrayed in pornographic films and videos, often as a way to close a scene.