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. Male masturbation may differ between males who have been circumcised and those who have not. Most soft crush fetishists avoid being placed under the same label as hard crush fetishists, believing that crush films with larger animals give the entire group a bad label. Pornographic films present sexual fantasies and usually include erotically stimulating material such as nudity. Performers are usually clean-shaven, thinner and more effeminate than ones in mainstream gay pornography. It is commonly depicted in pornography, but very rarely in mainstream hentai porn cinema. This style of filming is in contrast to having a separate, third-person camera gay bear porn crew filming all the action. Given the wide range of practices, some of which may be engaged in by people who do not consider themselves as practicing BDSM, inclusion in the BDSM community or subculture is usually dependent on self-identification and shared experience. Using the term shemale for a transsexual woman often implies that she is working in the sex trade. 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. Failure to honor a safeword is considered serious misconduct and could even change the sexual consent situation into a crime, depending on the relevant law, since the bottom has explicitly revoked his or her consent to any actions that follow the use of the safeword . There is no singular or archetypical behavior; therefore, a wide range of thought patterns and behaviors exist, but all tends to be a harmless and efficacious release from some kind of pressure. Going back at least as far as the Christy twins in the 1970s, depictions of incest and particularly incest between twins has been a feature of gay pornography.