Mutual masturbation, mutual manual stimulation of the genitals between partners, can be a substitute for sexual penetration. Behind the Green Door was one of the first pornographic films to feature sex between a white actress with a black actor . Gay pornography is the representation of sexual activity between males. The term comes from the French voyeur, one who looks. Often other friends and community members may witness the signing of such a document in a ceremony, and so parties violating their agreement can result in loss of face, respect or status with their friends in the community. Common phrases used to refer to these individuals are chicks with dicks or the derogatory term shemale, although these are generally considered pejorative among transwomen. 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. However, various videos gays groups within society considered such depictions immoral, labelling them pornographic, and attempting to have them suppressed under obscenity laws, with varying degrees of success. There is, however, no third party camera hentai videos work involved. Bukkake is a sex act portrayed in pornographic films, in which several men ejaculate on a woman, or another man. Sub-genres can also be classified into the characteristics lesbian milfs of the performers or the type of sexual activity on which it concentrates, and not necessarily on the market to which each sub-genre appeals. 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. Mammary intercourse is known as titty-fucking, titfuck, or a titjob in the United States, as well as tit wank or French fuck in the United Kingdom - the latter term dating back to the 1930s; while a more jocular equivalent is a trip down mammary lane.