The interaction between tops and bottoms—where physical or mental control of the bottom is surrendered to the top—is sometimes known as power exchange, whether in the context of an encounter or a relationship. Various groups within society have considered mature milfs depictions of a sexual nature immoral, labeling them pornographic, and attempting to have them suppressed under obscenity and other laws, with varying degrees of success. Felching involves drinking recently ejaculated semen from the vagina or anus. Buck Angel is the best-known actor in this genre. Bukkake videos are a relatively prevalent niche in contemporary gay fuck pornographic films. Bestiality pornography involves the sexual attraction of humans to animals. 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. Voyeur or peeping Tom pornography is usually more staged with the subjects aware of the cameras, sometimes openly including this exhibitionist awareness. The fundamental principles for the exercise of BDSM require that it should be performed with the informed consent of all involved parties. Pegging is a recently invented word which features a woman penetrating a man with 3d hentai a strap-on dildo. In the 1920s, Havelock Ellis reported that turn-of-the-century seamstresses using treadle-operated sewing machines could achieve orgasm by sitting near the edge of their chairs. It is also often mixed with other fetishes in practice, such as voyeurism, denial, etc. Boot fetishism is a sexual fetish dedicated to boots. The most established and probably most cliché set form of dominance and submission is Dominance and slavery. Though the term anal sex most commonly means penile-anal penetration, sources sometimes use the term anal intercourse to refer exclusively to penile-anal penetration, and anal sex to refer to any form of anal sexual activity, especially between pairings as opposed to anal masturbation.