Body parts including fingers, tongue and penis may be used for anonymous oral, vaginal and/or anal intercourse. Although pornography has usually focused on heterosexuality, due to the prevalence of the heterosexual orientation, explicit gay material has a long history as well, which reaches back to Greek antiquity, if not to prehistory. English adopts and uses hentai as a genre of pornography by the commercial sale and marketing of explicit works under this label. The term soft crush refers to the more common fetish surrounding videos involving inanimate objects or small invertebrates being crushed, while the term hard crush refers to such videos involving larger animals with vertabrae, and arguably more pain-susceptible animals . These agreements are binding in the sense that the parties have the expectation that the negotiated rules will be followed. The term lesbian is also used with regard to sexual identity or sexual behavior, regardless of sexual orientation, or as an adjective to characterize or associate nouns with female homosexuality or same-sex attraction. It may be used as foreplay, or as an alternative to sexual penetration. The stigma of being gay or labeled as such has steadily eroded since the Stonewall riots began the modern American gay rights movement in 1969. This technique may include the use of a simulacrum, or artificial vagina. It is sometimes combined with BDSM features. A few extremely flexible males can reach and stimulate their penis with their gay sex video tongue or lips, and so perform autofellatio. Real enema shots or videos of true medical situations may violate privacy laws in some countries. Animal masturbation has been observed in many species, both in the wild and in captivity. Snuff pornography involves the actual death of any of the participants, consenting or otherwise, simulated lesbian hentai death is not considered snuff. The scenario is a genre of erotica, which on the internet is sometimes abbreviated horny milfs to CMNF, and may involve sexual and nonsexual erotic scenarios.