The preference could be barefoot, high-heels, flip flops, and so on, depending on the fetishist. Special forms include erotic roleplay like ageplay, in which a difference in age, either real or enacted, formulates gay fuck the background; or petplay. Today, pornographic films can be sold or rented on DVD, shown through Internet and special channels and pay-per-view on cable and satellite, and in adult theaters. Reading or viewing pornography, sexual fantasy or other erotic stimuli may lead to a desire for sexual release such as by masturbation. In humans, females generally have more round and voluptuous buttocks, caused by estrogen that encourages the body to store fat in the buttocks, hips, and thighs. Some people get sexual pleasure by inserting objects, such as urethral sounds, into the urethra , a practice known as urethral play or sounding. Some people masturbate by using machines that simulate intercourse. Group sex also occurs in populations of non-human animals such as bonobo apes and chimpanzees. Reality pornography is a genre of pornography where staged scenes, usually shot in cinéma vérité fashion, set up and precede sexual encounters. Pegging films include Strap It On , Babes Balling Boys , Strap Attack, Strap-on Sirenz, Strap-on Chicks, Boss Bitches , various movies produced by LEDA Studios, and San Francisco-based Men In Pain. Cartoon pornography depicts illustrated or lesbian milfs animated fictional characters in erotic and sexual situations. Jeffrey Masson has even argued that incest porn is the very nucleus of pornography — its prototypical form. Locks may be used to emphasize the submissive position or the submissive hands may be fastened above his head to the box. In recent years, however, many celebrities have benefited from the publicity resulting from the hentai videos release of a sex tape. Cheerleader pornography involves pictures of cheerleaders, both staged and real. People may also find masturbating with friends helps lift the stigma they feel surrounding the act. Unlike smothering, in facesitting the bottom partner is not deprived of air.