Sadomasochism refers to the aspects of BDSM surrounding the exchange of physical or emotional pain. Production of such films was profitable, and a number of producers specialised in their production. Bukkake pornography involves a performer, usually female, onto whom several men or women ejaculate, usually on the face. Such grounds and even the definition of pornography have differed in various historical, cultural, and national contexts. In some creampie films, both gay and straight, intercourse and internal ejaculation are followed by performers licking up nude milfs the semen that has dripped hentai movies from their bodies. The fantasy is typically based around one or more larger beings dominating a smaller being. Shotacon : Similar to Lolicon, this genre involves prepubescent or under-aged boys between the ages 6–12. These actors often play the top roles but this is not always the case, such as with Kristen Bjorn and some Bel Ami models. Creampie, also known as internal cum shot, and, in homosexual contexts, also known as breeding and seeding, is a slang term used in pornography to describe when a male ejaculates inside his partner vagina or anus. Studies among BDSM practitioners in the US have shown that about half of all men find the idea of bondage to be erotic; many women do as well. Among swinging couples, one of the two partners is often the driving force and the other is more passive-supportive of the addition of additional sex parties. Such works have also often been subject to censorship and other legal restraints to publication, display or possession. Following the introduction of the Motion Picture Association of America film rating system, independent animation producers attempted to establish an alternative to mainstream animation. Creampie pornography features ejaculation inside the vagina , mouth or rectum instead of the common cum shot, followed by the visible seeping or dripping of semen from the vagina, mouth or gaysex anus. Diaper fetishism, nappy fetishism or diaperism, is a sexual fetish in which a person feels a desire to wear or use diapers.