It may involve sexual attraction to women who are pregnant or appear pregnant, attraction to lactation, or attraction to particular stages of pregnancy such as impregnation or childbirth. The anus has a relatively high concentration of nerve endings and can be an erogenous zone, and the receiver may receive pleasure from external anal stimulation. Bobbi S. Within a BDSM or D/s context, facesitting can be an especially intense form of erotic humiliation. Rough sex pornography is similar to pornography featuring sadomasochism, and typically features a Top who humiliates and/or degrades a Bottom while being physically violent towards them. One or more of the participants may engage in autoerotic sexual activity, such as masturbation, possibly without physical contact with the other participants. Consent is the most important criterion here. Bisexual DVDs sell much better online than in adult video stores, possibly due to customers in stores feeling embarrassed to buy them. The 1979 U. Interracial pornography typically employs ethnic and racial stereotypes in its depiction of performers and many of interracial pornographic films still include racial stereotypes, although the segregation of actors by race has diminished considerably. There were also a very limited number of specialist fetish magazines which featured images of hentai videos bondage, such as the famous Bizarre magazine published from lesbian milfs 1946 to 1959 by the pioneering fetish gay movies photographer John Willie, and ENEG Exotique magazine, published 1956-1959. Twink pornography features younger performers, and usually features young men under 30 who identify as gay or bisexual. As in B/D, the declaration of the Top/Bottom may be required, though sadomasochists may also play without any Power Exchange at all, with both partners equally in control of the play. Others involve partners who naturally have a significant difference in size. Bisexual pornography is a genre of pornography which most typically depicts one woman and two men who all perform sex acts on each other.