It is difficult to watch Director Steve McQueen’s “12 Years a Slave” without looking away from the screen every so often. Lynched, murdered, raped, sold, traded, and owned: these are verbs we never want to associate with human existence. But it’s undeniable that these acts are a part of our legacy as Americans. And it’s utterly painful. It doesn’t play into our national denial, like “Lincoln,” by marginalizing the black experience by lionizing white political leaders, or like “Django Unchained” by reimagining the past as a Spaghetti Western. McQueen (“Hunger,” “Shame”) mounts horrifying images of the shredded backs, twitching feet, floating bodies, and chained limbs atop another to give a glimpse into the lives of slaves lived in constant fear and oppression. With strong performances by the incredible Chiwetel Ejiofor in the title role, Lupita Nyong’o, and Michael Fassbender among many, McQueen delivers one of the greatest films about American slavery and the need to own up to our checkered past.