Foot fetishism has been defined as a pronounced sexual interest in the feet or footwear. Group sex pornography features at least two men and two women , usually more, who all perform sex acts on each other. Works in this genre may be considered adult for any number of reasons. Studies have found that masturbation is frequent in humans of both sexes and all ages, although there is variation. Hermaphrodite, also known as herm, refers to pornography, typically hentai, that features persons with the genitalia of both sexes. Biological anthropologist Helen B. Medical pornography involves sexualized medical, often fake, including gynecological pelvic examinations, rectal examinations, and pelvic or gynecological gay boy porn ultrasounds. Ass to mouth is a slang term primarily milf fuck used to describe the withdrawal hentai sex of a penis from the receptive partner anus followed by the immediate insertion into the receptive partner mouth. 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. Femdom features BDSM scenes in which the dominant partner is female. Contrary to the other two types, B/D does not define the Tops and Bottoms itself, and is used to describe the general activities with either partner being the receiver and the giver. Some are aroused from wetting their diapers, others like messing their diapers. Macrophilia is a fascination with or a sexual fantasy involving giants, more commonly expressed as giantesses . Bondage pornography specializes in the depiction of sexual bondage or BDSM activities as photographs, stories, movies, or drawings. A celebrity can fight the release in court to maintain deniability while still enjoying the career benefits. Specific sex acts Anal Anal pornography features anal penetration with a penis, dildo, other objects, or some combination of them. By comparison, gonzo pornography puts the camera right into the action, often with one or more of the participants both filming and performing sexual acts, without the usual separation between camera and performers seen in conventional porn and cinema.