The fundamental principles for the exercise of BDSM require that it should be performed with the informed consent of all involved parties. Rough sex pornography is similar to pornography featuring sadomasochism, and typically features a Top who humiliates and/or degrades a Bottom while being physically violent towards them. Although gay twink porn pornography has usually focused on heterosexuality, due to the prevalence of the heterosexual orientation, explicit gay material has a long history as well, which reaches back to Greek antiquity, if not to prehistory. Actors are mostly amateur; any well-known actors in bisexual porn tend to be from the gay pornography industry. A facial is a form of non-penetrative sex, though it is generally performed after some other means of sexual stimulation, such as vaginal sex, anal sex, oral sex or masturbation. Pleasure for the giver during anilingus is usually based more on the principle of the act. It is mutual consent that makes a clear legal and ethical distinction between BDSM and such crimes as sexual assault or domestic violence. Pornographic films present sexual fantasies and usually include erotically stimulating material such as nudity. Male masturbation may differ between males who have been circumcised and those who have not. 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. The person sat upon may be in bondage, sexually submissive, or simply held down by the body-weight of the other person. This technique may include mature milfs the use of a simulacrum, or artificial vagina. Strictly speaking, bondage means binding the partner by tying their appendages together; for example, by the use of handcuffs or by lashing their arms to an object. Given the wide range hentai sex of practices, some of which may be engaged in by people who do not consider themselves as practicing BDSM, inclusion in the BDSM community or subculture is usually dependent on self-identification and shared experience.