A sexual fantasy or erotic fantasy is a mental image or pattern of thought that stirs a person's sexuality and can create or enhance sexual arousal. A sexual fantasy can be created by the person's imagination or memory, and may be triggered autonomously or by external stimulation such as erotic literature or pornography, a physical object, or sexual attraction to another person. Anything that may give rise to a sexual arousal may also produce a sexual fantasy, and sexual arousal may in turn give rise to fantasies. Sexual fantasies are nearly universal, being reported in many societies across the globe. However, because of the nature of some fantasies, the actual putting of such fantasies into action is far less common, due to cultural, social, moral, and religious constraints. In some cases, even a discussion by a person of sexual fantasies is subject to social taboos and inhibitions. Some people find it convenient to act out fantasies through sexual roleplay. A person may find validation of a sexual fantasy by viewing the depiction or discussion of the fantasy in film, usually of a pornographic nature. A fantasy may be a positive or negative experience, or even both. It may be in response to a past experience and can influence future sexual behavior. A person may not wish to enact a sexual fantasy in real life, and since the process is entirely imaginary, they are not limited to acceptable or practical fantasies, which can provide information on the psychological processes behind sexual behavior. Sexual fantasy can also pertain to a genre of literature, film or work of art. Such works may be appreciated for their aesthetics, though many people may feel uncomfortable with such works. For example, women in prison films may be described as sexual fantasies, as are pornographic films. In the case of films, the term may describe a part of the film, such as a fantasy scene or sequence. Besides pornographic films, a number of mainstream films have included sexual fantasy scenes, such as Business Is Business (1971), Amarcord (1973), American Beauty (1999) and others. In many cases, the use of fantasy scenes enables the inclusion of material into a work indicating the sexualised mental state of a character. Methodology It is difficult to objectively identify and measure the nature of sexual fantasies, so that many studies deal with conscious fantasies when a person is awake, using one of