Going back at least as far as the Christy anime hentai twins in the 1970s, depictions of incest and particularly incest between twins has been a feature of gay pornography. The padding may also muffle noises from the outside, causing a relaxation effect and heightening their other senses. Many men who like trans partners of any variety, known as tranny chasers, do not necessarily identify as gay themselves. Such films continued to be produced but could only be distributed by underground channels. This may relate to fetishes such as voyeurism or cuckolding. Bukkake, Gokkun, Omorashi, and tentacle erotica are few uniquely Japanese genres known to western viewers. The term is a slang word that originated in the gay community and comes from the equestrian term bareback, which refers to the practice of riding a horse without a saddle. Fisting involves the insertion of one partner entire hand into a vagina or the anal cavity. This gay cock category also includes pornographic home movies. Fisting pornography features the insertion of an entire hand into a performer vagina or anus. Depictions of male and female masturbation are common in pornography, including gay pornography. Sex experts have praised various techniques that the performer can use during fellatio to increase their partner pleasure. When sexual activity is centered on one of the threesome, then the activity may be described as a gang bang of the person. Bisexual DVDs sell much better online than in adult video stores, possibly due to customers in stores feeling embarrassed to buy them. Entacle erotica describes a type of pornography most commonly found in Japan which integrates traditional pornography with elements of bestiality and a fantasy, horror, mature milfs or science-fiction theme. Some restrict a policy of panties/nipple tape for females and some allow full nudity with explicit sexual interaction allowed. In some societies, the terms fox, plum, chick, or chicken are preferred. Bisexual pornography is a genre of pornography which most typically depicts one woman and two men who all perform sex acts on each other.