These agreements are binding in the sense that the parties have the expectation that the negotiated rules will be followed. Masturbation has been depicted in art videos porno gay since prehistoric times and is mentioned and discussed in very early writings. Guro or Gore is a genre of Japanese pornography involving blood, gore, disfiguration, violence, mutilation, urine, enemas, or feces. The consent and compliance for a sadomasochistic situation can be granted only by people who can judge the potential results. Consent is the most important criterion here. In the context of consensual erotic activities, sadism and masochism are not strictly accurate terms; there is a significant difference from the medical or psychological usage of both terms. The sub-genres usually conform to certain conventions, and each may appeal to a particular audience. Body parts naked milf including fingers, tongue and penis may be used for anonymous gay hentai oral, vaginal and/or anal intercourse. Others involve partners who naturally have a significant difference in size. It may involve sexual attraction to women who are pregnant or appear pregnant, attraction to lactation, or attraction to particular stages of pregnancy such as impregnation or childbirth. Unlike the traditional definition of the term, in fetish usage a cuckold is complicit in their partner sexual infidelity and takes masochistic sexual pleasure in it. Ethnic pornography is a genre of pornography that features performers of specific ethnic groups, or depictions of interracial sexual activity. Spanking or whipping pornography involves spanking or whipping, generally of the buttocks, with the hand or with other objects such as belts, switches, paddles, brushes, or whips. Lesbianism has been a theme in erotic art since at least the time of ancient Rome, and many regard depictions of lesbianism to be erotic. Some techniques which may work for one individual can be difficult or uncomfortable for another. Mammary intercourse is said by Alex Comfort to produce mutual orgasm in women with sensitive breasts , and it was one of the nine substitute exercises for penetrative sexual activities, as detailed in the Paradis Charnels of 1903.