An Encyclopedia states that "the inner third of the anal canal is less sensitive to touch than the outer two-thirds, but is more sensitive to pressure" and that "the rectum is a curved tube about eight or nine inches long and has the capacity, like the anus, to expand". In pornography, anal sex is commonly portrayed as a desirable, painless routine that does not require personal lubricant ; this can result in couples performing anal sex without care, and men and women believing that it is unusual for women, as receptive partners, to find discomfort or pain instead of pleasure from the activity. The latter was allowed because anal intercourse was considered equivalent to vaginal intercourse in this way; men were said to "take it like a woman" muliebria pati, "to undergo womanly things" when they were anally penetrated, but when a man performed anal sex on a woman, she was thought of as playing the boy's role. This is sometimes termed technical virginity. What data we do have almost all relate to penetrative sexual acts, and the superficial contact of the anal ring with fingers or the tongue is even less well documented but may be assumed to be a common sexual activity for men of all sexual orientations. A study found that Researchers say adequate application of a personal lubricant, relaxation, and communication between sexual partners are crucial to avoid pain or damage to the anus or rectum. It is also common for subject review panels and schools to avoid the subject. Those who enjoy either role may be referred to as versatile. Anecdotally, it is a substantial number. They used condoms during anal sex Because of this, some couples practice anal intercourse as a form of contraception , often in the absence of a condom. Seducing those not of proper age for example, non-adolescent children into the practice was considered very shameful for the adult, and having such relations with a male who was no longer adolescent was considered more shameful for the young male than for the one mounting him; Greek courtesans, or hetaerae , are said to have frequently practiced male-female anal intercourse as a means of preventing pregnancy. The Larco Museum houses an erotic gallery in which this pottery is showcased. For example, besides the risk of HIV transmission being higher for anal intercourse than for vaginal intercourse,    the risk of injury to the woman during anal intercourse is significantly higher than the risk of injury to her during vaginal intercourse because of the durability of the vaginal tissues compared to the anal tissues. McBride's clinical review on heterosexual anal intercourse and other forms of anal sexual activity, it is suggested that changing norms may affect the frequency of heterosexual anal sex. Research has found that psychological factors can in fact be the primary contributors to the experience of pain during anal intercourse and that adequate communication between sexual partners can prevent it, countering the notion that pain is always inevitable during anal sex.