In the 18th and 19th centuries, some European gay twink porn theologians and physicians described it as heinous, deplorable, and hideous, but during the 20th century, these taboos generally declined. The term is typically used by the cinematographer within the narrative framework of a pornographic film, and since the 1970s has become a leitmotif of the hardcore genre. Bondage pornography specializes in the depiction of sexual bondage or BDSM activities as photographs, stories, movies, or drawings. Biological anthropologist Helen B. A study of 164 males in Finland from two SM clubs found that 18.2% had engaged in coprophilia; 3% as a sadist, 6.1% as a masochist, and 9.1% as both. 18% of heterosexuals and 17% of homosexuals in the study pool had tried coprophilia, showing no statistically significant difference between heterosexuals and homosexuals. The activity is done by itself or as a part of or prelude to other activities which many times hentai porn involve sex. Coprophilia , also called scatophilia or scat , is the paraphilia involving sexual arousal and pleasure from feces. Patricia Hill Collins, an African-American writer, theorizes that this is derived from a stereotype that those of black descent are promiscuous, and their buttocks are objectified by porn as a result. Perhaps following the example set by gay pornography, they have become a popular subgenre within heterosexual pornography since the turn of the century, featuring both vaginal and anal ejaculations. Lying face down one may use the hands, one may straddle a pillow, the corner or edge of the bed, a partner leg or some scrunched-up clothing big tit milf and hump the vulva and clitoris against it. Some masturbate only using pressure applied to the clitoris without direct contact, for example by pressing the palm or ball of the hand against underwear or other clothing. A study of the condom usage habits of New Zealand sex workers said that they offered various safe sex alternatives to vaginal sex to clients who refused to wear a condom. Breast fetishism is a paraphilic sexual interest focused on female breasts .