Sadism describes sexual pleasure derived by inflicting pain, degradation, humiliation on another person or causing another person to suffer. Following the introduction of the Motion Picture Association of America film rating system, independent animation producers attempted to establish an alternative to mainstream animation. Spanking can be administered in a number of spanking positions. As a form of non-penetrative sex, it can be done for its own enjoyment or as foreplay. Use of the agreed safeword is seen by some as an explicit withdrawal of consent. Since mammary intercourse is a non-penetrative sex act, the risk of passing a sexually transmitted infection that requires direct contact between the mucous membranes and pre-ejaculate or semen is greatly reduced. In S/M, the Sadist is usually the Top and the Masochist the Bottom, but these roles are frequently more complicated or jumbled . Arcane or occult pornography involves sexualized situations with an occult or magical tone or performers who costume themselves in keeping with the theme, for example, a male performer dressed as a wizard. Its gain in prominence has been attributed to its depiction in the film Pecker, which was released in 1998. Specific sex acts Anal Anal pornography features anal penetration with a penis, dildo, other objects, or some combination of them. Works in this genre may explore philosophical, political or social issues. Detective magazines, comic books and early fetish magazines In the early 20th century, Detective magazines covertly provided a way of publishing bondage imagery. Types of anal sex can also be a part of lesbian sexual practices. Common positions include lying on back or face down, sitting, squatting, gay videos kneeling or standing. Although there may be no connection between coprophilia and sadomasochism , the limited data on the former comes from studies of the latter. A bisexual threesome may involve a man having sex with a man and a woman, the woman having sex with a man and a woman, or all three having sex with each other.