Horror films have always been great carriers for social commentary. The tropes, the carnage, the acceptance that characters on screen are going to put themselves in risky situations—it all allows for the message to go down easy. Actor/producer Kurtis David Harder’s directorial debut, “Spiral,” is a solid example of the way this works, though it’s more than just a timely cultural critique. In this horror film, the horror is our history, our treatment of minorities. It’s a bold and terrifying story, but it’s told with all the usual bells and whistles, basements and attics, creaks and bangs.