Bukkake pornography involves a performer, usually female, onto whom several men or women ejaculate, usually on the face. Spanking can be administered in a number of spanking positions. Group sex also occurs in populations of non-human animals such as bonobo apes and chimpanzees. However, various groups within society considered such depictions immoral, gay bear porn labelling them pornographic, and attempting to have them suppressed under obscenity laws, with varying degrees of success. The genre presents itself as real couples having real sex. 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. Following the introduction of the Motion Picture nude milfs Association of America film rating system, independent animation producers attempted to establish an alternative to mainstream animation. Female masturbation involves the stroking or rubbing of a woman vulva, especially her clitoris, with an index or middle fingers, or both. Yaoi is anime or manga that features gay males . Internal ejaculation shots are a comparatively hentai porn recent development in pornography; they are not found in early pornographic films. This type of pornography is almost exclusively hentai, as true hermaphroditic humans are not fertile and are not usually found in nature. In contrast, a celebrity may take the route of openly releasing the tape and benefit directly from royalties as well as indirectly from the publicity. Breeding is sometimes followed by felching, which involves sucking the semen from the partner anus. Cartoon pornography depicts illustrated or animated fictional characters in erotic and sexual situations. This makes varying degrees of stimulation an integral part of oral sex for many men. The resulting consent and understanding is occasionally summarized in a written contract, which is an agreement of what can and cannot take place.