Ghostly rationality

Poor ghosts, poor ghosts! how many flights they must have attempted for two hundred years from their hated sins, how many excuses they must have given for their presence, and the sins were with them still—and still unexplained. Suddenly one of them seemed to scent my living blood, and bayed horribly, and all the others left their ghosts at once and dashed up to the sin that had given tongue. The brute had picked up my scent near the door by which I had entered, and they moved slowly nearer to me sniffing along the floor, and uttering every now and then their fearful cry. I saw that the whole thing had gone too far. But now they had seen me, now they were all about me, they sprang up trying to reach my throat; and whenever their claws touched me, horrible thoughts came into my mind and unutterable desires dominated my ​heart. I planned bestial things as these creatures leaped around me, and planned them with a masterly cunning. A great red-eyed murder was among the foremost of those furry things from whom I feebly strove to defend my throat. Suddenly it seemed to me good that I should kill my brother. It seemed important to me that I should not risk being punished. I knew where a revolver was kept; after I had shot him, I would dress the body up and put flour on the face like a man that had been acting as a ghost. It would be very simple. I would say that he had frightened me—and the servants had heard us talking about ghosts. There were one or two trivialities that would have to be arranged, but nothing escaped my mind. Yes, it seemed to me very good that I should kill my brother as I looked into the red depths of this creature's eyes. But one last effort as they dragged me down—"If two ​straight lines cut one another," I said, "the opposite angles are equal. Let AB, CD, cut one another at E, then the angles CEA, CEB equal two right angles (prop. xiii.). Also CEA, AED equal two right angles."

I moved towards the door to get the revolver; a hideous exultation arose among the beasts. "But the angle CEA is common, therefore AED equals CEB. In the same way CEA equals DEB. Q.E.D." It was proved. Logic and reason re-established themselves in my mind, there were no dark hounds of sin, the tapestried chairs were empty. It seemed to me an inconceivable thought that a man should murder his brother.

 -- Lord Dunsany, "The Ghosts," from The Sword of Welleran and Other Stories (1908)