Sigmund Freud considered foot binding as a form of fetishism. The industry generally refers to such films as adult films, which is part of adult entertainment. This type of pornography is almost exclusively hentai, as true hermaphroditic humans are not fertile and are not usually found in nature. Both sexes sometimes apply lubricating substances to intensify sensation. The strategies and tactics that are used to smuggle one of the couple into and out of the toilet undetected are as important or almost as important as the urination. Real medical shots or videos may violate privacy gay twinks laws in some countries. For example, in Australia it is rated Refused Classification . The other person may do the same during or after. 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. Both forms of pornography generally contains nudity. 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. Content featuring male bisexuality has been a growing trend since the advent of internet pornography. John Stagliano is considered to have started the gonzo pornography genre with his Buttman series of films. Many cultures describe pain as an aphrodisiac. Detective magazines, comic books and early fetish magazines In the early 20th century, Detective magazines covertly provided a way of publishing bondage imagery. Bestiality is illegal hentai movies in many countries. Bondage websites and bondage imagery in mainstream pornography As of 2003, specialist bondage magazines were mostly displaced by the availability of bondage material on the World Wide Web, and the presence of bondage imagery in mainstream pornographic magazines such as Nugget and Hustler Taboo magazine. In some scenes or relationships it may be impossible for consent to be withdrawn in the middle of a scene, horny milfs or the bottom may have the ability to revoke consent for a relationship as a whole, but not for a particular scene.