Derivative academic Fields of study may both interact with and develop independently of filmmaking, as in film theory and analysis. Fields of academic study have been created that are derivative or dependent on the existence of film, such as film criticism, film history, divisions of film propaganda in authoritarian governments, or psychological on subliminal effects of a flashing soda can during a screening. These fields may further create derivative fields, such as a movie review section in a newspaper or a television guide. Sub-industries can spin off from film, such as popcorn makers, and toys. Sub- industries of pre-existing industries may deal specifically with film, such as product placement in advertising.