Such grounds and even the definition of pornography have differed in various historical, cultural, and national contexts. They may be noted for using risqué themes, graphic violence, sexuality or black comedy in a manner that is unsuitable for younger audiences. HIV is among the infections that require such direct contact and is therefore very unlikely to be transmitted via mammary intercourse. Some people masturbate momsex by using machines that simulate intercourse. Cartoon pornography includes, but is not limited to, hentai and parody renditions of famous cartoons and comics. This makes varying degrees of stimulation an integral part of oral sex for many men. This genre also features male-on-male fellatio through a small hole made in a bathroom divider. It is the most common form of sexual fetishism for otherwise non-sexual objects or body parts. Women with women Main article: Lesbianism in erotica: Lesbianism in contemporary pornography Lesbian or girl-girl pornography features women engaged in sex together, but is typically aimed at a male audience. Some anthropologists and sociobiologists believe that breast fetishism derives from the breasts similarity to buttocks, but instead provide sexual attraction from the front of the body. Additionally, the buttocks gay movies give an indication of the shape and size of the pelvis, which impacts reproductive capability. The loose and direct camera work hentai porn often includes tight shots of the genitalia, unlike some traditional porn. The name was coined from the title of the controversial book. In the gay pornography industry, which uses amateurs as well as professional actors, the term gay-for-pay refers to actors labeled or believed to be straight but who engage in same-sex sexual activities for money. The two sets of people involved often meet either randomly or arrange to meet up beforehand over the Internet. Some people get sexual pleasure by inserting objects, such as urethral sounds, into the urethra , a practice known as urethral play or sounding.