Fear is an autonomic response triggered by unpleasant stimuli that causes increased heart rate, muscle tension, and rapid breathing. While fear reactions are not consciously controlled, they serve an evolutionary purpose of avoiding risks that could end our lives. The Legend of Sleepy Hollow by Washington Irving was an early work of American literature that used fear and the supernatural to tell the ghost story of a headless horseman. Other authors have since adapted and expanded on the themes of fear in works of Gothic and children's horror literature.