In both stories the eye is a significant symbol. In the Tell-Tale Heart it is what makes the narrator kill the old man and in the Black Cat the missing eye is what reminds him of the old cat and makes him mad at the new cat. Also in the Black Cat the cat itself symbolises that something bad will happen. In the beginning the narrator's wife states that all black cats are witches in disguise. This makes the mood dark and mysterious.
In both stories Poe uses first person