Poe is heavy on the symbolism, and he often repeats symbol use from one story to the next. For example, in "The Masque of the Red Death," when an ebony clock housed in a black and blood-red room strikes midnight, all the revelers at the masquerade stop and tremble in fear, as though they fear their own mortality. In "The Tell-Tale Heart," the narrator spies on the old man with whom he lives just at midnight every night for a week, waiting for the opportune moment to kill him. He even confesses to often being awake at that hour himself, listening to the deathwatch beetles ticking in the walls and groaning in "mortal terror." We soon learn that he, too, fears his own death and must rid himself of the old man because the old man is, himself, a reminder of the narrator's own mortality. In both stories, midnight, as the death of day, is symbolic of mortality, as is the clock and the color black from "Masque." This color symbolism resurfaces in Poe's poem "The Raven," because the raven is black and also signifies our mortality and the inevitability of death. You can see, even just from these few examples, that Poe also often takes mortality as a major theme of his writing.