There are no particular or preferred elements within maiesiophilia that are common to all maiesiophiliacs. The padding may also muffle noises from the outside, causing a relaxation effect and heightening their other senses. As in B/D, the declaration of the Top/Bottom may be required, though sadomasochists may also play without any Power Exchange at all, with both partners equally in control of the play. The fundamental principles for the exercise hentai sex of BDSM require that it should be performed with the informed consent of all involved parties. Rape itself is a crime in many countries. Going back at least as far as the Christy twins in the 1970s, depictions of incest and particularly incest between twins has been a feature of gay pornography. Pornography can be classified according to the physical characteristics of the participants, fetish, sexual orientation, etc., as well as the types of sexual activity featured. Sometimes special furniture is used, such as a queening stool or smotherbox. Unlike erotic films, pornographic films contain explicit sexuality and do not claim any artistic merit. This is commonly called double anal or double stuffing. Pornography is generally classified as either softcore or hardcore pornography. Exhibitionist pornography features performers, usually female exposing themselves in public and spans simple flashing to public sex. The films were financially successful, winning AVN Awards for the best selling pornographic films of their year; however the events were effectively un-officiated and the record breaking claims often misleading. BDSM has milf fuck become an umbrella term for certain kinds of erotic behavior hot gay sex between consenting adults. BDSM pornography depicts bondage and discipline, domination and submission, sadism and masochism. Ethnic pornography is a genre of pornography that features performers of specific ethnic groups, or depictions of interracial sexual activity. 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.