Patricia Hill Collins, an African-American writer, theorizes that this is derived from a stereotype that milf xxx those of black descent are promiscuous, and their buttocks are objectified by porn as a result. Medical pornography involves sexualized medical, often fake, including gynecological pelvic examinations, rectal examinations, and pelvic or gynecological ultrasounds. Bukkake is a sex act portrayed in pornographic films, in which several men ejaculate on a woman, or another man. Foot fetishism has been defined as a pronounced sexual interest in the feet or footwear. In POV porn, the shooting style is generally similar to gonzo pornography, with the person receiving sexual gratification holding the camera him or herself—aiming it down at the actress or actor who is performing the sex act. A celebrity can fight the release in court to maintain deniability while still enjoying the career benefits. Studies have found that masturbation is frequent in humans of both sexes and all ages, although there is variation. The term pearl necklace is used by some because the drops of semen deposited by the man resemble a necklace of translucent white pearls. Preggo pornography features pregnant performers and may include erotic lactation as a fetish. The naked appearance of actress Demi Moore in the advanced stage of pregnancy on the cover of Vanity Fair magazine in 1991 marked the beginning of a period which has since seen pregnancy presented by celebrities as a glamorous state of living, while also creating a market for photographers to produce images of pregnant mothers, and for fashion stylists to introduce pregnancy styling to their business. It is geared towards heterosexual men, who most typically define a threesome as such. This makes varying degrees of stimulation an integral part of oral sex for many men. Typically featured are hitting, choking, name-calling and hair-pulling. Older names for a pornographic film include stag film, and blue movie. A study of gay fuck 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, anime hentai showing no statistically significant difference between heterosexuals hentai tentacle porn and homosexuals.