In the film industry, unsimulated sex is the presentation in a film of sex scenes where the actors engage in a genuine sex act rather than miming or simulating the actions. At one time in the United States such scenes were restricted by law and self-imposed industry standards such as the Motion Picture Production Code. Films showing explicit sexual activity were confined to privately distributed underground films, such as stag films or "porn loops". Beginning in the late 1960s, most notably with Blue Movie by Andy Warhol, mainstream movies began pushing boundaries in terms of what was presented on screen. Although the vast majority of sexual situations depicted in mainstream cinema is simulated (in early pornography, the main actors engaged in simulated sex, with inserts placed in the film