The cat looked up at him for a moment, smiling in its ecstasy, blinking its eyes, but too happy to pause. He spoke to it again. He called to it several times, and each time it turned upon him its blazing eyes, drunk with inner delight, opening and shutting its lips, its body large and rigid with excitement. Yet it never for one instant paused in its short journeys to and fro.

He noted exactly what it did: it walked, he saw, the same number of paces each time, some six or seven steps, and then it turned sharply and retraced them. By the pattern of the great roses in the carpet he measured it. It kept to the same direction and the same line. It behaved precisely as though it were rubbing against something solid. Undoubtedly, there was something standing there on that strip of carpet, something invisible to the doctor, something that alarmed the dog, yet caused the cat unspeakable pleasure.

“Smokie!” he called again, “Smokie, you black mystery, what is it excites you so?”