The latest film from Andrea Arnold (Red Road, Fish Tank, American Honey) is a feature-length documentary about a cow, starring a cow, with almost nothing else in it, apart from this cow. It feels like a test. Can I watch a cow for 93 minutes? What does this cow do that’s so interesting? I see cows all the time from the train and they just sort of lounge about, ruminating, don’t they? But this wants you to look, really look, at what it is to be a cow.