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. A heterosexual threesome may involve two men and a woman, or one man and two women - that is, two men having sex with a woman , or two women with a man. Some anthropologists and mature milfs sociobiologists believe that breast fetishism derives from the breasts similarity to buttocks, but instead provide sexual attraction from the front of the body. Studies have found that masturbation is frequent in humans of both sexes and all ages, although there is variation. Coprophilia , also called scatophilia or scat , is the paraphilia involving sexual arousal and pleasure from feces. Low et al. Such video tapes are often released without the consent of their subjects, and could potentially damage celebrities careers. Creampie pornography features ejaculation inside the vagina , mouth or rectum instead of the common cum shot, followed by the visible seeping or dripping of semen from the vagina, mouth or anus. A hentai sex person may be sexually penetrated multiple times simultaneously. Top and dominant are widely recognized for those partner in the relationship or activity who are, respectively, the physically active or controlling participants. There are various subcultures under this umbrella term and distinct difference between these subcultures. Some prefer a particular type of clothing gaysex to urinate. Such works have also often been subject to censorship and other legal restraints to publication, display or possession. A bisexual threesome may involve a man having sex with a man and a woman, the woman having sex with a man and a woman, or all three having sex with each other. 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. Although there may be no connection between coprophilia and sadomasochism , the limited data on the former comes from studies of the latter.