His already twisted mind was fed by alcohol for too long and his ability to think clearly was reduced to its minimum. But there is always the possibility of him seeing Pluto and his successor as the witches in disguise, as has been hinted in the story, too. The disdain felt towards anything supernatural could force, again combined with liquor, him to decide to get rid of the evil powers. In addition, he did not torture the other animals in the same manner he decided to persecute the cats.
The Tell-Tale Heart and The Black Cat are both short stories with rather unreliable narrators who like to twist the reality. And like with a crooked mirror, it is hard to distinguish what is real and what is only visible due to the material defect. It is therefore up to the reader to decide what is relevant and what has been altered in order to appeal to the audience more. Everyone might interpret the two stories differently, even though they for sure have one element in common –