There are many reasons Francis Bacon's Figure with Meat bothers the mind. It's a crazed smear of flesh, velvet, and bone, but I think it lingers mostly because the screaming bishop inhabits a zone that cannot be determined, a room etched only by a few ghostly chalk lines. The ambiguity forces us to supply our own nightmares that pulse in the murk just beyond the grasp of language. Which is the whole point of painting, I think. And perhaps horror, too.
