Incest itself is largely taboo, and is a crime in many countries. Biological anthropologist Helen B. Pornography is often distinguished from erotica, which consists of the portrayal of sexuality with high-art aspirations, focusing also on feelings and emotions, while pornography involves the depiction of acts in a sensational manner, with the entire focus on the physical act, so as to arouse quick intense reactions. The volume of semen that is ejaculated depends on several factors, including the male health, age, degree of sexual excitement, and the time since his last ejaculation. Solo performances in gay pornography have been described in 1985 as either or both active and/or passive , whereas female solo performances are said to be exclusively passive . Pornography may fall into gay movies more than one genre. When the interest in a particular subject is obsessive, momsex the behavior may be described as stalking. Films with risqué content commenced to be produced soon after the invention of the motion picture in the 1880s. A survey by the New York City Department of Health and Mental Hygiene found that heterosexual women are more likely to bareback when engaging in anal sex than homosexual and bisexual men. Some anthropologists and sociobiologists believe that breast fetishism derives from the breasts similarity to buttocks, but instead provide sexual attraction from the front of the body. The term sadomasochism is derived from the words sadism and masochism . Hardcore pornography is pornography that depicts penetration or extreme fetish acts, or both. Some people get sexual pleasure by inserting objects, such as urethral sounds, into the urethra , a practice hentai sex known as urethral play or sounding. The most common type of erotic spanking is administered on the bare buttocks, but can also be combined with bondage, in order to heighten sexual arousal and feelings of helplessness. However, bisexual pornography is often placed near the gay section in adult video stores, since many consumers are gay men.