Its gain in prominence has been attributed to its depiction in the film Pecker, which was released in 1998. Special forms include erotic roleplay like ageplay, in which a difference in age, either real or enacted, formulates the background; or petplay. It is typically animated pornography, as the legal age to be featured in a pornographic film in Japan is 18. Snowballing or snowdropping is the human sexual practice in which one person takes someone else semen into his or her mouth and then passes it to the mouth of the other, usually through kissing. Mutual masturbation, mutual manual stimulation of the genitals between partners, can be a substitute for sexual penetration. In these research publications, it is suggested that real female ejaculation is the release of a very scanty, thick, and whitish fluid from the female prostate, while the squirting or gushing shown frequently in pornography is a different phenomenon, the expulsion of clear and abundant fluid, which has been shown to be a diluted fluid from the urinary bladder. The loose and direct camera work often includes momsex tight shots of the genitalia, unlike some traditional porn. In general, as compared to conventional relationships, BDSM participants go to great lengths to negotiate the important aspects of their relationships in advance, and to take great care in learning about and following safe practices. For some people, non-penetrative sex is the primary sexual activity of choice above all others. 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. Women with women Main article: Lesbianism in erotica: Lesbianism in contemporary pornography Lesbian or girl-girl pornography features women engaged in sex together, but is typically aimed at a male audience. Clothed female, naked male pornography features naked 3d hentai men and clothed gay fuck women; typically, the women humiliate and abuse the men or perform fellatio and/or handjobs on the men.