Erotic spankings are commonly combined with other forms of sexual foreplay. Mammary intercourse has sometimes been considered a perversion. In Japan, point of view pornography is referred to as hamedori . The niche popularity grew significantly in the latter half of the first decade of the 2000s. Reading or viewing pornography, sexual fantasy or other erotic stimuli may lead to a desire for sexual release such as by masturbation. See nude milfs also Gay-for-pay. The most successful animated features produced in the United States primarily for adult audiences hentai porn were directed by Ralph Bakshi, including Fritz the Cat, Heavy Traffic hot gay sex and Coonskin. The primary subjects of pornographic depictions are pornographic models, who pose for still photographs, and pornographic actors or porn stars, who perform in pornographic films. Voyeurism is the sexual interest in or practice of spying on people engaged in intimate behaviors, such as undressing, sexual activity, or other actions usually considered to be of a private nature. 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. Mutual masturbation foreplay The manual stimulation of each other genitals where the session eventually leads to sexual intercourse. Hentai narrow Japanese usage and broad international usage are often incompatible. The term BDSM dates back to 1969; however, the origin of the term BDSM is unclear and is believed to have been formed either from joining the term B&D with S&M , or as a compound initialism from B&D, D&S , and S&M. Snowballing or snowdropping is the human sexual practice in which one person takes someone else semen into his or her mouth and then passes it to the mouth of the other, usually through kissing. The term is typically used by the cinematographer within the narrative framework of a pornographic film, and since the 1970s has become a leitmotif of the hardcore genre.