Partners can engage in penetrative sex, known as full swap, or choose to soft swap in which they engage only in non-penetrative sex. Arguably the most famous example of the genre is the Taboo series. Teacher and Student or Boss and Secretary pornography involves sexualized situations which take place between an authority figure, such as a teacher or boss, and an underling, such as a student or secretary, often fake. Especially popular in post-World War 2 Japanese culture. For other scenes, particularly in established relationships, a safeword may be agreed to signify a warning rather than explicit withdrawal of consent; and a few choose not to use a safeword at all. The sub-genres usually conform to certain conventions, and each may appeal to a particular audience. Although macrophilia literally translates to simply a lover of large, in the context of a sexual fantasy it is used to mean someone who attracted to beings larger than themselves. In pornography, depictions of lesbian sex form a popular subgenre, directed toward a male heterosexual and female homosexual audience. Can also include auto-fellatio, or performing oral sex on oneself. RACK may be seen as focusing primarily momsex upon awareness and informed consent, rather than accepted safe practices. Actors are mostly amateur; any well-known actors in bisexual porn tend to be from the gay pornography industry. Initially, few animation studios in the United States attempted to produce animation for adult audiences, but later examples of animation produced for adults would gain mainstream attention and success. The higher pay scale and profile within a production often leads to group scenes where a straight actor only tops. Technically this is a form of exhibitionism rather than group sex per se. Pornography is generally classified as either softcore hentai movies or hardcore gay sex video pornography. Erotic spanking is the act of spanking another person for the sexual arousal or gratification of either or both parties. The nipples are erogenous zones, and vigorous stimulation of them during masturbation usually causes the penis to become erect more quickly than it would otherwise.