Babysitter pornography features usually teenage girls being exploited and having taboo sex with older, male employers. Some restrict a policy of panties/nipple tape for females and some allow full nudity with explicit sexual interaction allowed. Others may also use vibrators and other sexual devices more commonly associated with female masturbation. The genres of pornography are based on the type of activity featured and the category of participants, for example mateur pornography is a category of pornography that features models, actors or non-professionals performing without pay, or actors for whom this material is their only paid modeling work. Facial cum shots are currently regularly portrayed in pornographic films and videos, often as a way to close a scene. The concept of lesbian, to differentiate women with a shared sexual orientation, is a 20th-century construct. Generally, interest differs between people, and gender depends on sexual orientation. Sexologist Alfred Kind suggested that the buttocks is the primary sexual presentation site in primates. As in B/D, the declaration of the Top/Bottom may be required, gaysex though sadomasochists may also play without any Power Exchange at all, with both partners equally in control of the play. Targets the male audience, celebrity sex tapes but is much less popular than Yaoi. Such films continued to be produced but could only be distributed by underground channels. Snuff pornography involves the actual death of any of the participants, consenting or otherwise, simulated death is not considered snuff. A variant of A2M is ATOM where a performer inserts his penis directly from one recipient anus into a second recipient mouth. In human sexuality, a threesome is sexual activity that involves three people at the same time. Bisexual big tit milf pornography is a genre of pornography which most typically depicts mobile teen porn one woman and two men who all perform hentai videos sex acts on each other. Since the 1980s, many practitioners and organizations have adopted the motto safe, sane and consensual, commonly abbreviated as SSC, which means naked celebrities that everything is based on safe activities, that all participants be of sufficiently sound/sane mind to consent, and that all participants do consent.