Starting with erotic stories and woodblock prints from before the 20th century, Japanese pornography evolved into distinct subcategories with the media that in addition of pornographic videos and magazines featuring live actors, there is exist categories of pornographic manga , pornographic computer games , and pornographic anime . The term applies to the depiction of the act rather than the act gay hentai itself, and so does not include live exhibitions like sex shows and striptease. Sadomasochism is practiced in isolation relatively rarely, though some masochists report biting, pinching, or even stun-gunning themselves as a prelude to, or as part of, masturbation. There is no singular or archetypical behavior; therefore, a wide range of thought patterns and behaviors exist, but all tends to be a harmless and efficacious release from some kind of pressure. The definition clash also appears with the English gay sex video definition of yuri as any lesbian relationship, as opposed to its sexually explicit definition in Japan. Entacle erotica describes a type of pornography porn milf most commonly found in Japan which integrates traditional pornography with elements of bestiality and a fantasy, horror, or science-fiction theme. The term hentai is never used in this context in Japanese. Animal masturbation has been observed in many species, both in the wild and in captivity. Because the viewing of such films carried a social stigma, they were viewed at brothels, adult movie theaters, stag parties, at home, in private clubs and also at night cinemas. The inside of a smotherbox is often padded to provide support for their neck and prevent their head from moving. Bondage/BDSM Bondage pornography features performers tied up or constrained in various ways. Transsexual porn star Wendy Williams has stated that transsexual porn is classified as Straight Specialty. Sexologist Alfred Kind suggested that the buttocks is the primary sexual presentation site in primates. Transgender pornography features performers who cross-dress for sexual gratification, either for themselves or for their partners.