Depictions of male and female masturbation are common in pornography, including gay pornography. Bisexual pornography is a genre of pornography which most typically depicts one woman and two men who all perform sex acts on each other. Rainbow parties were covered on The Oprah Winfrey Show in hentai videos 2003, and became the subject of a juvenile novel called Rainbow Party. The original definition of dogging – and which is still a closely related activity – is spying on couples having sex in a car or other public place. Common positions include lying on back or face down, sitting, squatting, kneeling or standing. The definition clash also appears with the English definition of yuri as any lesbian relationship, as opposed to its sexually explicit definition in Japan. A few extremely flexible males can reach and stimulate their penis with their tongue or lips, and so perform autofellatio. 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. Since development and pronunciation of the buttocks begins at menarche and declines with age, full buttocks are also a symbol of youth. Entacle erotica describes a type of pornography most commonly found in Japan which integrates traditional pornography with elements of bestiality and a fantasy, horror, or science-fiction theme. Mammary intercourse is a sex act, performed as foreplay or as non-penetrative sex, that involves the stimulation of the male penis by the female breasts and vice versa. It is commonly depicted in pornography, but very rarely in mainstream cinema. Because the viewing of such films carried a social stigma, they were viewed at brothels, adult movie theaters, stag parties, momporn at home, in private gay cock clubs and also at night cinemas. It is sometimes combined with BDSM features. Urolagnia is a form of salirophilia in which sexual excitement is associated with the sight or thought of urine or urination.