It may also involve touching, rubbing, big tit milf or pinching the nipples or other erogenous zones while masturbating. While bondage is a very popular variation within the larger field of BDSM, it is nevertheless sometimes differentiated from the rest of this field. Mammary intercourse is said by Alex Comfort to produce mutual orgasm in women with sensitive breasts , and it was one of the nine substitute exercises for penetrative sexual activities, as detailed in the Paradis Charnels of 1903. The principal characteristic of voyeurism is that the voyeur does not normally interact directly with the subject of his/her interest, who is often unaware of being observed. In many cases, that person is also aroused by smelling body parts that have a urine scent. In the context of consensual erotic activities, sadism and masochism are not strictly accurate terms; there is a significant difference from the medical or psychological usage of both terms. It is suggested that much of the obscurity and the uncertainties about female ejaculation are related to mixing up these two phenomena. The buttocks in human females thus contain more adipose tissue than in males, especially after puberty. Shibari is a Japanese word that literally means to tie or to bind. A large part of hentai movies the popularity of celebrity porn these gay fuck videos is seeing how regular and normal the girls are in real-life. 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. Real enema shots or videos of true medical situations may violate privacy laws in some countries. Mutual masturbation can be practiced by males or females in pairs or groups with or without actually touching another person as indicated by the following examples of contact versus non-contact scenarios: Non-contact mutual masturbation Two people masturbating in the presence of each other but not touching.