Reflective of its views on sexuality and culture, Japanese pornography delves into a wide spectrum of heterosexual, homosexual, and transgender sexual acts in addition to unique fetishes and philias. Some do not use the diapers at all, for arousal, or bladder and bowel movements. The buttocks in human females thus contain more adipose tissue than in males, especially nude milfs after puberty. Tentacle rape or shokushu goukan is found in some horror or hentai titles, with tentacled creatures having sexual intercourse with female characters. Watersports pornography features sexual activities involving urine, such as golden showers. This may relate to fetishes such as voyeurism or cuckolding. As with most forms of sexual activity, anal sex participants risk contracting sexually transmitted infections . 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. Greater economic and social freedom allowed them gradually to be able to determine how they could form relationships and families. Bhabha, Anne McClintock and Kobena gay movies Mercer. The anus has a relatively high concentration of nerve endings and can be an erogenous zone, and the receiver may receive pleasure from external anal stimulation. However the genre remains a very small proportion of the pornographic DVD market; for example at porn retailer HotMovies. Clothed female, naked male is a genre of erotica hentai sex featuring one or more nude men and one or more clothed women. It may also involve touching, rubbing, or pinching the nipples or other erogenous zones while masturbating. Making a pearl necklace is one of the activities that sex workers use as safe sex alternatives for people who refuse to wear condoms. The speed of the hand motion will vary from person to person, although it is not uncommon for the speed to increase as ejaculation nears and for it to decrease during the ejaculation itself. Softcore pornography generally contains nudity or partial nudity in sexually suggestive situations, but without explicit sexual activity, sexual penetration or extreme fetishism, while hardcore pornography may contain graphic sexual activity and visible penetration, including unsimulated sex scenes.