Both forms of pornography generally contains nudity. 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. Though there have been numerous gang bang pornographic films since the 1980s, they usually involved no more than half a dozen to a dozen men. Bondage pornography specializes in the depiction of sexual bondage or BDSM activities as photographs, stories, movies, or drawings. Pro-am pornography is sub-genre of amateur pornography that refers to professionally made porn that features amateur actors/actresses, often appearing for the first time in a pornographic film. Yaoi is anime or manga that features gay males . Examples of heterosexual pornographic film series gay movies featuring creampies include Cream Filled Teens and Internal Cumbustion. A pornographic work is characterized as hardcore if it has any hardcore content, no matter how small. Transsexual pornography is a genre of pornography. In general, BDSM play is usually structured such that it is possible for the consenting partner to withdraw his or her consent during a scene; for example, by using a safeword that was agreed on in advance. These actors often play the top roles but this is not always the case, such as with Kristen Bjorn and some Bel Ami models. Its gain in prominence has been attributed to its depiction in the film Pecker, which was released in 1998. Voyeur pornography may also include shots of topless women on topless beaches who are unaware of the cameras hentai movies but may legally be photographed due to the public setting. Some anthropologists and sociobiologists believe that breast fetishism derives from the breasts similarity to buttocks, but instead provide sexual attraction from the front of the body. Often, strong views are expressed with regard to anal sex; it is controversial in various cultures, especially with regard to religion, commonly due to prohibitions against anal sex among gay men or teachings about the procreative purpose of nude milfs sexual activity.