Horror/thriller movies were first established in the early 20th century to shock, thrill and terrify audiences by bringing their worst nightmares to life. Advances in technology and special effects have changed how horrors are made over time. Nowadays, horrors are also often mixed with other genres like comedy. Common conventions of horrors include terrifying characters, disturbing unexplained behavior, helpless victims, and psychotic killers. The level of gore and special effects used varies based on the type of horror, such as supernatural, psychological, or mystery thrillers.