Given the wide range of practices, some of which may be engaged in by people who do not consider themselves as practicing BDSM, inclusion in the BDSM community or subculture is usually dependent on self-identification and shared experience. Erotic literature and pornographic films have been devoted to the sexual uses of glory holes. Fisting, handballing, fist-fucking, brachiovaginal, or brachioproctic insertion is a sexual activity that involves inserting a hand into the vagina or rectum. Incest pornography is a genre of pornography involving the depiction of incest . Cum swapping pornography involves performers trading semen between their mouths. In the attempts of circumvent this type of censoring , actors and producers have featured subject matter unseen or rarely depicted in western pornography. Social attitudes towards the discussion and presentation of sexuality has become more tolerant and legal definitions of obscenity have become more limited, leading to an industry for the production and consumption of pornography in the latter half of the 20th century. Sexual arousal from a particular body part is classified as partialism. The effect is to give the viewer the sense that they are experiencing the sex acts that they are watching, as opposed to simply hentai movies watching others as a voyeur. The anal and rectal tissues are delicate and do not provide natural lubrication, so they can easily tear and permit disease transmission, especially if lubricant is not used. Also see POV. Another aspect is the structured training of the Bottom. In straight pornography, intercourse is often followed by a facial, pearl necklace or other visible ejaculation. Discipline young gay porn often incorporates sadomasochistic aspects, though some sadomasochists distance themselves from D/s practices such as punishment. The term shemale has been used since the mid-19th century, when it was a humorous colloquialism for female, especially an aggressive woman. Sex and relationship experts have varying definitions on how lesbian milfs the act is performed.