A horror film aims to frighten the audience and elicit feelings of fear. To be successful, it must contain at least one frightening element like the unknown, terror, torture or surrealism. If viewers feel scared by the film's content or characters, it is more likely to succeed commercially. Horror films commonly use conventions like dark lighting, eerie music, and vulnerable protagonists to build tension and unsettle audiences. They typically involve a threat murdering a group of people one by one until one survivor remains to defeat the threat.