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.