Spanking or whipping pornography involves spanking or whipping, generally of the buttocks, with the hand or with other objects such as belts, switches, paddles, brushes, or whips. Though the Christy twins may have been unrelated but similar-looking men and some twins have appeared together in scenes without substantial contact between them, some genuine twins have performed sexual acts on each other. Futanari, Hentai females with a penis. Freud, however, considered such extensions of sexual interest to fall within the range of the normal, unless marked out by exclusivity . As observation is encouraged, voyeurism hentai porn and exhibitionism are closely associated with dogging. Gonzo porn is influenced by amateur pornography, and it tends to use far fewer full-body/wide shots in favor of more close-ups . Cum hot gay sex swapping pornography involves performers trading semen between their mouths. Common phrases used to refer to these individuals are chicks with dicks, trannies, or shemales, although these are generally considered pejorative slurs among transwomen. Actors are mostly amateur; any well-known actors in bisexual porn tend to be from the gay pornography industry. Anti-pornography psychologist Ana Bridges and colleagues conducted a content analysis of best-selling heterosexual pornographic videos showing that over 96% of all scenes concluded with a male performer ejaculating onto the body of his female partner. Wetlook pornography involves clothed wet persons. Facesitting when a woman or a young girl sits on a man face. Central to the typical MILF narrative is milf fuck an age-play dynamic of older women and younger lovers. Erotic spanking is the act of spanking another person for the sexual arousal or gratification of either or both parties. Pornography can be classified according to the physical characteristics of the participants, fetish, sexual orientation, etc., as well as the types of sexual activity featured. Interracial pornographic films have experienced an explosion in popularity, becoming one of the fastest-growing and biggest-selling genres.