Studies have found that masturbation is frequent in humans of both sexes and all ages, although there is variation. Its gain in prominence has been attributed to its depiction in the film Pecker, which was released in 1998. Voyeurism is the sexual interest in or practice of spying on people engaged in intimate behaviors, such as undressing, sexual activity, or other actions usually considered to be of a private nature. A celebrity can fight the release in court to maintain deniability while still enjoying the career benefits. A study of 164 males in Finland from two SM clubs found gay hentai 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 consensual submission of the submissive is sometimes demonstrated to others by symbols indicating his/her belonging to the dominant, such as wearing a collar, special tattoos, piercings, a very short haircut or a bald head. Felching is a sexual practice involving the act of orally sucking semen out of the vagina or anus of one partner. A related term used in the genre is the term cougar, which implies an older woman as predator. Group sex pornography features at least two men and two women , usually more, momsex who all perform sex acts on each other. Such documents have not been recognized as being legally binding, nor are they intended to be. Positions can also be chosen specifically for added effects such as increased humiliation, elevation and suspension. 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 gay movies objectified by porn as a result. Such grounds and even the definition of pornography have differed in various historical, cultural, and national contexts. This type of pornography is almost exclusively hentai, as true hermaphroditic humans are not fertile and are not usually found in nature.