Final answer:
In the story 'The Tell-Tale Heart' by Edgar Allan Poe, the reason why the groan in the middle of the night sounds familiar to the narrator is not explained clearly, but it could be due to his heightened senses and paranoia.
Step-by-step explanation:
In the story 'The Tell-Tale Heart' by Edgar Allan Poe, the narrator hears a groan in the middle of the night that sounds familiar to him. The reason for this familiarity is not explicitly stated in the story, but it's implied that the groan reminds the narrator of a sound he has heard before. This could be a result of the narrator's heightened senses and increasing paranoia, causing him to associate the groan with a past experience or memory.