Works in this genre may be considered adult for any number of reasons. The purpose of this kind of agreement is primarily to encourage discussion and negotiation in advance, and then to document that understanding for the benefit of all parties. The term has origins in the Greek language . Cartoon pornography includes, but is not limited to, hentai and parody renditions of famous cartoons and comics. The introduction of the home video gay sex video and Internet saw a boom in the worldwide porn industry that generates billions of dollars annually. Unlike the usual power neutral relationships and play styles commonly followed by couples, activities and relationships within a BDSM context are often characterized by the participants taking on complementary, but unequal roles; thus, the idea of informed consent of both the partners becomes essential. In recent years, however, many celebrities have benefited from the publicity resulting from the release of a sex tape. HIV is among the infections that require such direct contact and is therefore very unlikely to be transmitted via mammary intercourse. Following the introduction of the Motion Picture Association of America film rating system, independent hentai videos animation producers attempted to establish an alternative to mainstream animation. Patricia Hill Collins, an African-American writer, theorizes that this is derived from a stereotype that those of nude milfs black descent are promiscuous, and their buttocks are objectified by porn as a result. The resulting consent and understanding is occasionally summarized in a written contract, which is an agreement of what can and cannot take place. This genre also features male-on-male fellatio through a small hole made in a bathroom divider. Yuri : Featuring two grown adult women in a homosexual/lesbian relationship. If one person is penetrated by two objects, it is generically called double penetration . However, gay pornography in the modern world is mostly concentrated in the making of home videos , cable broadcast and emerging video on demand and wireless markets, as well as images and movies for viewing on the Internet.