Pornography in Japan is large and intertwined business of adult entertainment with unique characteristics that readily distinguish it from western pornography. Mutual masturbation, mutual manual stimulation of the genitals between partners, can be a substitute for sexual penetration. There has been an increase in discussion and lesbian hentai portrayal of masturbation in art, popular music, television, films, and literature. Masturbation is the self-sexual stimulation of the genitals for sexual arousal or momporn other sexual pleasure, usually to the point of orgasm. Mammary intercourse is a sex act, performed as foreplay or as non-penetrative sex, that involves the stimulation of the male penis by the female breasts and vice versa. A woman can use a secondary vibrator, between the dildo and her genitals, to get pleasure from pegging. Real medical shots or videos may violate privacy laws in some countries. Older names for a pornographic film include stag film, and blue movie. Bukkake is a sex act portrayed in pornographic films, in which several men ejaculate on a woman, or another man. Certain websites have begun providing bondage videos and photographs featuring the kidnapping roleplay, which has been largely the hallmark of detective style bondage magazines. Both sexes sometimes apply lubricating substances to intensify sensation. Lying face down on a comfortable surface such as a mattress or pillow, the penis can be rubbed against it. Participants who exert sexual control over their partners are known as dominants or tops while participants who take the passive, receiving, or obedient role are known as submissives or bottoms. Following the introduction of the Motion Picture Association of America film rating system, independent animation producers attempted to establish an alternative to mainstream animation. Urolagnia is a form of salirophilia in which sexual excitement is associated with gay twinks the sight or thought of urine or urination. The term bondage describes the practice of Physical restraining.