Today, religions vary in their views of masturbation; some view it as a spiritually detrimental practice, some see it as not spiritually detrimental, and others take a situational view. The activity is done by itself or as a part of or prelude to other activities which many times involve sex. The current public acceptance of celebrities with sex tapes is speculated by Joe Levy, executive editor of Rolling Stone, to be due to the easy availability of pornography, as well as couples more commonly making their own tapes due to the prevalence of video cameras. This is commonly called double vaginal penetration or double stuffing. Biological anthropologist Helen B. Additionally, the buttocks give an indication of the shape and size of the pelvis, which impacts reproductive capability. Bukkake is a sex act portrayed in pornographic films, in which several men ejaculate on a woman, or another man. Diaper fetishism is totally independent from pedophilia as the wearer derives pleasure only from the diaper and/or use of it. To avoid soreness from this resulting friction, some may prefer to use a personal lubricant, masturbation cream or saliva during masturbation. As women, they face concerns separate from celebrity nude men. Patricia Hill Collins, an African-American writer, theorizes that this is derived from a stereotype that those of black descent are promiscuous, and their buttocks are objectified by porn as a result. In Japanese, the term describes any type of perverse or bizarre sexual desire or act; it does not represent a genre of work. This makes varying degrees of stimulation an integral part of oral sex for many men. Medical pornography involves sexualized medical, often fake, including gynecological pelvic examinations, rectal examinations, and pelvic or gynecological ultrasounds. Since mammary intercourse is a non-penetrative sex act, the risk of passing a sexually transmitted infection that requires direct contact between the mucous membranes and pre-ejaculate or semen is greatly reduced.