Although pornography has usually focused on heterosexuality, due to the prevalence of the heterosexual orientation, explicit gay material has a long history as well, which reaches back to Greek antiquity, if not to prehistory. Female ejaculation is the expulsion of fluid by the paraurethral ducts through and around the human female urethra during or before an orgasm. This category also includes pornographic home movies. There may be more than two participants; both group sex and gang banging can be included. Examples include the Girls Gone Wild and Girls Who Like Girls mature milfs Series. The term hentai is never used in this context in Japanese. Such explicit sexual interaction is seen only rarely in public play spaces, and it is sometimes specifically banned by gay twinks the rules of a party or playspace. These scenes may involve the female actor calling for the shot to be directed at some specific part of her body. The person sat upon may be in bondage, sexually submissive, or simply held down by the body-weight of the other person. Some BDSM practitioners prefer a code of behavior that differs from SSC and is described as risk aware consensual kink , indicating a preference for a style in which the individual responsibility of the involved parties is emphasized more strongly, with each participant being responsible for his or her own well-being. Going back at least as far as the Christy twins in the 1970s, depictions of incest and particularly incest between twins has been a feature of gay pornography. It may also involve touching, rubbing, or pinching the nipples or other erogenous zones while masturbating. Strictly speaking, bondage means binding the partner by tying their appendages together; for example, by the use of handcuffs or by lashing their arms to an object. Pornography is generally classified as either softcore or hardcore pornography. Failure to honor a safeword is considered serious misconduct and could even change the sexual consent situation into a crime, depending on the relevant law, since the bottom has explicitly revoked lesbian hentai his or her consent to any actions that follow the use of the safeword .