Today, religions vary in their views gaysex of masturbation; some view it as a spiritually detrimental momporn practice, some see it as not spiritually detrimental, and others take a situational view. Lying face down on a comfortable surface such as a mattress or pillow, the penis can be rubbed against it. Group sex pornography features at least two men and two women , usually more, who all perform sex acts on each other. A study of the condom usage habits of New Zealand sex workers said that they offered various safe sex alternatives to vaginal sex to clients who refused to wear a condom. A study of 164 males in Finland from two SM clubs found that 18.2% had engaged in coprophilia; 3% as a sadist, 6.1% as a masochist, and 9.1% as both. 18% of heterosexuals and 17% of homosexuals in the study pool had tried coprophilia, showing no statistically significant difference between heterosexuals and homosexuals. In S/M, the Sadist is usually the Top and the Masochist the Bottom, but these roles are frequently more complicated or jumbled . For some people, non-penetrative sex is the primary sexual activity of choice above all others. It is geared towards heterosexual men, who most typically define a threesome as such. Works in this genre may explore philosophical, political or social issues. People may experience pleasure from anal sex by stimulation of the anal nerve endings, and orgasm may be achieved through anal penetration – by indirect stimulation of the prostate in men, indirect clitoral/G-spot stimulation in women, and associated sensory nerves . This is commonly called double vaginal penetration or double stuffing. Some masturbate only using pressure applied to the clitoris without direct contact, for example by pressing the palm or ball of the hand against underwear or other clothing. Being forced to wear diapers as a form of humiliation is sometimes a behavior encountered in sexual masochism. The study also found that participants reacted hentai movies positively to a much wider range of figures than a control group, even rating emaciated figures higher.