The Black Cat by Edgar Allan Poe

This dread was not exactly a dread of physical evil—and yet I should be at a loss how otherwise to define it. I am almost ashamed to own—yes, even in this felon’s cell, I am almost ashamed to own—that the terror and horror with which the animal inspired me, had been heightened by one of the merest chimaeras it would be possible to conceive. My wife had called my attention, more than once, to the character of the mark of white hair, of which I have spoken, and which constituted the sole visible difference between the strange beast and the one I had destroyed. The reader will remember that this mark, although large, had been originally very indefinite; but, by slow degrees—degrees nearly imperceptible, and which for a long time my Reason struggled to reject as fanciful—it had, at length, assumed a rigorous distinctness of outline. It was now the representation of an object that I shudder to name—and for this, above all, I loathed, and dreaded, and would have rid myself of the monster had I dared—it was now, I say, the image of a hideous—of a ghastly thing—of the GALLOWS!—oh, mournful and terrible engine of Horror and of Crime—of Agony and of Death!
And now was I indeed wretched beyond the wretchedness of mere Humanity. And a brute beast —whose fellow I had contemptuously destroyed—a brute beast to work out for me—for me a man, fashioned in the image of the High God—so much of insufferable wo! Alas! neither by day nor by night knew I the blessing of Rest any more! During the former the creature left me no moment alone; and, in the latter, I started, hourly, from dreams of unutterable fear, to find the hot breath of the thing upon my face, and its vast weight—an incarnate Night-Mare that I had no power to shake off—incumbent eternally upon my heart!
Beneath the pressure of torments such as these, the feeble remnant of the good within me succumbed. Evil thoughts became my sole intimates—the darkest and most evil of thoughts. The moodiness of my usual temper increased to hatred of all things and of all mankind; while, from the sudden, frequent, and ungovernable outbursts of a fury to which I now blindly abandoned myself, my uncomplaining wife, alas! was the most usual and the most patient of sufferers.