Horror films strive to elicit emotions of fear, disgust and horror from viewers through unsettling scenes involving the macabre and supernatural. Early silent horror films from the 1920s took surreal, dark approaches influenced by expressionist art and theater of the time. The 1930s saw a rebirth of horror movies with the advent of sound film, which added new dimensions of terror through music, footsteps and monster sounds. By the 1950s, the concept of horrific monsters had changed from creatures to more human faces of evil representing issues of the time like nuclear weapons and the Holocaust.