"But… what are the horses for?" I explained patiently. "There is a law in this country against killing a man unless you have a horse on him. When two or more men are throwing dice for the drinks, you will often hear one of them say, 'horse on you' or 'horse on me.' You can't kill a man unless you say that before he does. Another thing you'll hear a man say, if he finds out something is only a hoax, he'll call it a mare's nest, because it's full of mares and no horses. Still another trouble is a horse's feathers. In case it has feathers —" "What is a mare?" I cleared my throat. "The opposite of a horse. As you know, everything must have its opposite. There can't be a right without a left, or a top without a bottom, or a best without a worst. In the same way there can't be a mare without a horse or a horse without a mare. If you were to take, say, ten million horses —"