In "The Black Cat" the narrator describes his actions as "rapping heavily" upon the brick wall with a cane.
The narrator has clearly lost his mind at this point in the story. As the police comes to visit and check the premises to find evidence of what could have caused the murder of the woman, all checks out in favor of the main character. Therefore, the narrator gets arrogant at seeing that he may be able to get away with the murder. He starts then making a scene where he taps on the bricks, showing that his house and cellar are "well built". This was all part of his insanity. Then he hears a howl coming from within the wall. The policemen hear the sound as well, break the wall, and find the body of the woman, along with a cat trapped inside the wall next to her corpse. This cat's cry gave away the secret, and the narrator was found out.Hope this helped=)
