It may be regarded as taboo or unnatural, and is a criminal offense in some countries, punishable by corporal or capital punishment; by contrast, people also regard anal sex as a natural and valid form of sexual activity that may be as equally fulfilling as any other desired sexual expression. Real enema shots or videos of true medical situations may violate privacy laws in some countries. As a result, little in history was documented to give an accurate description of how female homosexuality is expressed. Actual upskirt or downblouse shots may violate privacy laws in some countries. 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. There may be more than two participants; both group sex and gang banging can be included. Amateur porn has been called one of the most profitable and long-lasting genres of pornography. A variant of A2M is ATOM where a performer inserts his penis directly from one recipient anus into a second recipient mouth. He talked to them extensively on camera so that both he and the viewer can come to know them before any sex scenes. These scenes may either have the cameraman directly engaging in sex or merely filming others having sex. The term soft crush refers to the more common fetish surrounding videos involving inanimate objects or small invertebrates being crushed, while the term hard crush refers to such videos involving larger animals with vertabrae, and arguably more pain-susceptible animals . Ass to mouth pornography shows the transfer of a performer penis from a second performer anus to that same second performer mouth in a single shot. There is hentai movies also some evidence that pornography can be used to treat voyeurism. 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. Pornography is often referred gay twink porn to as porn and a pornographic naked milf work as a porno.