Initially, few animation studios in the United States attempted to produce animation for adult audiences, but later examples of animation produced for adults would gain mainstream attention and success. The nipples are erogenous zones, and vigorous stimulation of them during masturbation usually causes the penis to become erect more quickly than it would otherwise. Some productions are noted for sophisticated and/or experimental storytelling and animation techniques. Ethnic pornography is a genre of pornography that features performers of specific ethnic groups, or depictions of interracial sexual activity. High heel pornography involves women or men dressed in high heeled shoes. The stimulation may involve hands, fingers, everyday objects, sex toys or combinations of these. As with most forms of sexual activity, anal sex participants risk contracting sexually transmitted infections . Gonzo porn is influenced 3d hentai by gay fuck amateur pornography, and it tends to use far fewer full-body/wide shots in favor of more close-ups . Teacher and Student or Boss and Secretary pornography involves sexualized nude milfs 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. There is also some evidence that pornography can be used to treat voyeurism. A facial is a form of non-penetrative sex, though it is generally performed after some other means of sexual stimulation, such as vaginal sex, anal sex, oral sex or masturbation. Some BDSM practitioners prefer a code of behavior that differs from SSC and is described as risk aware consensual kink , indicating a preference for a style in which the individual responsibility of the involved parties is emphasized more strongly, with each participant being responsible for his or her own well-being. After the prerequisite level of sexual stimulation has been achieved, and ejaculation becomes imminent, the male will position his penis so that the semen discharged will be deposited onto his partner face.