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. As well as traditional attraction, the topic also incorporates feederism and gaining, where sexual gratification is obtained via the process of gaining body fat. There are various subcultures under this umbrella term and distinct difference between these subcultures. Pornographic films are produced and supplied on a variety of media, depending on demand and the technology available, including traditional film stock in various formats, video for home viewing, DVD, Internet download, cable TV and other media. The term has origins in the Greek language . Such grounds and even the definition of pornography have differed in various historical, cultural, and national contexts. 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. Today, pornographic films can be sold or rented on DVD, shown through Internet and special channels and pay-per-view on cable and satellite, and in adult theaters. The purpose of this kind of agreement is primarily to encourage discussion and negotiation in advance, and then to document that understanding for the benefit of all parties. Gay pornography is the representation of sexual activity porn milf between males. Tentacle erotica features lesbian hentai tentacled creatures raping or otherwise penetrating women or men. A person may be sexually penetrated multiple times simultaneously. Some people masturbate by using machines that simulate intercourse. Production of such films was profitable, and a number of producers specialised in their production. Matsuo started working in the genre in 1991, saying that this intimate hot gay sex technique was a natural way for him to shoot in order to show his feelings for the girl and to get her to open up about herself, to show her true emotions.