While anal sex is commonly associated with male homosexuality, research shows that not all gay males engage in anal sex and that it is not uncommon in heterosexual relationships. Irrespective of the legal or social view of pornography, it has been used in a number of contexts. Since mammary intercourse is a non-penetrative sex act, the risk of passing a sexually transmitted infection that requires direct contact between the mucous membranes and pre-ejaculate or semen is greatly reduced. 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. Masturbation is the self-sexual stimulation of the genitals for sexual arousal or other sexual pleasure, usually to the point of orgasm. Bondage websites and bondage imagery gay boy porn in mainstream pornography As of 2003, specialist bondage magazines were mostly displaced by the availability of bondage material on the World Wide Web, and the presence of bondage imagery in mainstream pornographic magazines such as Nugget and Hustler Taboo magazine. A pornographic work is characterized as hardcore if it has any hardcore content, no matter how small. Pregnancy fetishism is a context where pregnancy is seen by individuals or cultures as an erotic phenomenon. Biological hentai sex anthropologist Helen B. Commenting on why there are not as many female macrophiles, psychologist Helen Friedman theorized that because women in most societies already view men as dominant and powerful, there no need for them to mature milfs fantasize about it. Group sex pornography features at least two men and two women , usually more, who all perform sex acts on each other. Women oriented pornography is sometimes referred to as sex positive pornography. A celebrity can fight the release in court to maintain deniability while still enjoying the career benefits. Group sex most commonly takes place in a private sex party or semi-public swinger gathering, but may also take place at massage parlors or brothels or, in some jurisdictions, at purpose-built locations such as sex clubs.