Saliva pornography involves salivation and saliva. The principal characteristic of voyeurism is that the voyeur does not normally interact directly with the subject of his/her interest, who is often unaware of being observed. The Japanese sex industry uses the term Paizuri . See Gay-for-pay. Softcore pornography generally contains nudity or partial nudity in sexually horny milfs suggestive situations, but without explicit sexual activity, sexual penetration or extreme fetishism, while hardcore pornography may contain graphic sexual activity and visible penetration, including unsimulated sex scenes. It can be combined with fellatio and the woman may move her breasts up and down on the penis for an additional stimulation, hentai sex usually before the man reaches orgasm. Mutual masturbation is a sexual act where two or more people stimulate themselves or one another sexually, usually with the hands. It spawned numerous sequels, several of which won adult film awards. In pornography, depictions of lesbian sex form a popular subgenre, directed toward a male heterosexual and female homosexual audience. As in B/D, the declaration of the Top/Bottom may be required, though sadomasochists may also play without any Power Exchange at all, with both partners equally in control of the play. Transsexual porn star Wendy Williams has stated that transsexual porn is classified as Straight Specialty. This category also includes pornographic gay twinks home movies. Group sex can occur between people of all sexual orientations and genders. 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. By Japanese law, the genitals of actors and actresses must be censored and up the mid-1990 so was the depiction of pubic hair. Caro rejected that as being a necessary conclusion, stating that female fatty deposits on the hips improve individual fitness of the female, regardless of sexual selection.