Works in this genre may explore philosophical, political or social issues. Felching is a sexual gay twinks practice involving the act of orally sucking semen out of the vagina or anus of one partner. Such grounds and even the definition of pornography have differed in various historical, cultural, and national contexts. Yuri : Featuring two grown adult women in a homosexual/lesbian horny milfs relationship. The genre presents itself as real couples having hentai porn real sex. Arcane or occult pornography involves sexualized situations with an occult or magical tone or performers who costume themselves in keeping with the theme, for example, a male performer dressed as a wizard. Positions can also be chosen specifically for added effects such as increased humiliation, elevation and suspension. A woman can use a secondary vibrator, between the dildo and her genitals, to get pleasure from pegging. Barebacking usually refers to a conscious and deliberate choice to forgo condoms. In Japanese, the term describes any type of perverse or bizarre sexual desire or act; it does not represent a genre of work. A 2009 study found that heterosexual male fat admirers preferred females that were clinically overweight and rated both overweight and obese women more positively than slighter individuals. Evolutionary psychologists suggest that rounded buttocks may have evolved to be desirable trait because they provide a visual indication of the woman youth and fertility. Rubber pornography involves rubber, latex, and similar materials. The fantasy is typically based around one or more larger beings dominating a smaller being. Some POV/gonzo porn sometimes breaks the strict point-of-view convention. Group sex pornography features at least two men and two women , usually more, who all perform sex acts on each other. The introduction of the home video and Internet saw a boom in the worldwide porn industry that generates billions of dollars annually. Some people get sexual pleasure by inserting objects, such as urethral sounds, into the urethra , a practice known as urethral play or sounding.