FOR A MOMENT I thought it was a shadow passing through the long grass. I hadn’t seen a black rabbit for years. It stopped, and standing on hind legs, listened to the May breeze. The sun came out and lit its fur to a blackberry gloss.Science refers to this randomly occurring genetic mutation as melanism. Sensing no danger, the rabbit began to feed. Gradually, the rest of the warren, all the usual brown, emerged until it was like a page from Watership Down. A black rabbit occurs in one of cinema’s most moving scenes, the cartoon death of Watership Down’s heroic buck, Hazel. When Hazel, after many self-sacrificing adventures, is nearing his time, weary and broken with years, a strange rabbit comes to him. “You’ve been feeling tired,” the stranger sympathis