BDSM has become an umbrella term for certain kinds of erotic behavior between consenting adults. Teacher and Student or Boss and Secretary pornography involves sexualized situations which take place between an authority figure, such as a teacher or boss, and an underling, such as a student or secretary, often fake. Masturbation has been depicted in art since prehistoric times and is mentioned and discussed in very early writings. Some couples use pornography at times for variety and to create a sexual interest or as part of foreplay. When he is in position the cover is closed. Bestiality pornography involves the sexual attraction of humans to animals. Sometimes special furniture is used, anime hentai such as gaysex a queening stool or smotherbox. 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. Actors are mostly amateur; any well-known actors in bisexual porn tend to be from the gay pornography industry. The stimulation may involve hands, fingers, everyday objects, sex toys or combinations of these. Along with the penis, the scrotum is sensitive and considered to be an erogenous zone. Other forms nude milfs of anal sex include fingering, the use of sex toys for anal penetration, oral sex performed on the anus , and pegging. 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. In some societies, the terms fox, plum, chick, or chicken are preferred. Male masturbation may differ between males who have been circumcised and those who have not. Participants usually derive pleasure from this, even though many of the practices—such as inflicting pain or humiliation or being restrained—would be unpleasant under other circumstances. Some couples use a threesome as a way to develop a love triangle .