Depictions of male and female masturbation are common in pornography, including gay pornography. Along with the penis, the scrotum is sensitive and considered to be an erogenous zone. It may involve sexual attraction to women who are pregnant or appear pregnant, attraction to lactation, or attraction to particular stages of pregnancy such as impregnation or childbirth. In September 2003 the BBC reported on the new dogging craze. Consent is the most important criterion here. The sub-genres usually conform to certain conventions, and each may appeal to a particular audience. BDSM actions can often take place during a specific period of time agreed to by both parties, referred to as play, a scene or a session. Shibari is a Japanese word that literally means to tie or to bind. The buttocks in human females thus contain more adipose tissue than in males, especially after puberty. As with most forms of sexual activity, anal sex participants risk contracting sexually transmitted infections . By Japanese law, the genitals of actors and actresses must be censored and up the mid-1990 so was the depiction of pubic hair. This is commonly called double milf fuck anal or double stuffing. This technique may include the use of a simulacrum, or artificial vagina. Internal ejaculations, followed by images of semen dripping from the anus, are sometimes depicted in bareback gay pornography, where they are gay movies referred to by the term breeding or the reverse money shot. Mutual masturbation can be practiced by males or females in pairs or groups with or without actually touching another person as indicated by the following examples of contact versus non-contact scenarios: Non-contact mutual masturbation Two people masturbating in the presence of each other but not touching. Within a hentai porn BDSM or D/s context, facesitting can be an especially intense form of erotic humiliation. 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.