Body parts including fingers, tongue and penis may be used for anonymous oral, vaginal and/or anal intercourse. Pornographic films present sexual fantasies and usually include erotically stimulating material such as nudity. For other scenes, particularly in established relationships, a safeword may be agreed to signify a warning rather than explicit withdrawal of consent; and a few choose not to use a safeword at all. It is mutual consent that makes a clear legal and ethical distinction between BDSM and such crimes as sexual assault or domestic violence. As observation is encouraged, voyeurism and exhibitionism are closely associated with dogging. Freud, however, considered such extensions of sexual interest to fall within the range of the normal, unless marked out by exclusivity . Enema pornography involves adults gay sex video given enemas to others, often fake. Partners can engage in penetrative sex, known as full swap, or choose to soft swap in which they engage only in non-penetrative sex. Matsuo used amateur actresses in his videos, and he usually traveled to their hometowns for the filming. As of 2010, they were reported to live together as a monogamous couple outside of their porn careers and want to continue working together for another 50 years. This is commonly called double anal or double stuffing. Erotic spanking is the act of spanking another person for the sexual arousal or gratification of either or both parties. Transsexual porn star Wendy Williams has stated that transsexual porn is classified as Straight Specialty. Twink pornography features younger performers, and usually features naked milf young men under 30 who identify as gay or bisexual. The anus has a relatively high concentration of nerve endings and can be an erogenous zone, and the receiver may receive pleasure from external anal stimulation. In some areas, there are laws stating it is not legally possible to consent to be killed, and elsewhere it may still be legally hentai movies dubious . One or more of the participants may engage in autoerotic sexual activity, such as masturbation, possibly without physical contact with the other participants.