There are films that entertain, films that move, and then there are films that crack open your skull and peer into the abyss. Joshua Oppenheimer’s The Act of Killing falls squarely into the latter category. It’s not a horror film, though it will likely haunt you more than any jump scare or blood-soaked monster. It’s a documentary, a unflinching look into the Indonesian genocide of 1965-66, and a descent into the psyche of the killers themselves.