For legal momsex reasons, the vast majority of so-called reality porn involves professional actors and actresses posing as so-called amateurs. Tentacle rape or shokushu goukan is found in some horror or hentai titles, with tentacled creatures having sexual intercourse with female characters. A homosexual threesome would involve either three men or three women. Mammary intercourse is said by Alex Comfort to produce mutual orgasm in women with sensitive breasts , and it was one of the nine substitute exercises for penetrative sexual activities, as detailed in the Paradis Charnels of 1903. Incest itself is largely taboo, and is a crime in many countries. The term applies to the depiction of the act rather than the act itself, and so does not include live exhibitions like sex shows and striptease. The Silent Duck, also called Duck-Billing, is the technique often used in which the person engaging in hand insertion shapes the hand to resemble a duck beak. Advocates of RACK argue that SSC can hamper discussion of risk because no activity is truly safe, and that discussion of even low-risk possibilities is necessary for truly informed consent. Comic books often featured 3d hentai characters being tied up and tying others up, particularly in damsel in distress plots. Gloryhole pornography features women performing fellatio on unidentified men through a small hole made in a bathroom divider. Facial cum shots are currently regularly portrayed in pornographic films and videos, often as a way to close a scene. For much of the history of cinema and television, lesbianism was considered videos gays taboo, though since the 1960s it has increasingly become a genre in its own right. It is mutual consent that makes a clear legal and ethical distinction between BDSM and such crimes as sexual assault or domestic violence. Pornography is often referred to as porn and a pornographic work as a porno. Lesbian pornography made for women is usually made by women, and usually features women who identify as lesbian or bisexual.