The narrator shows his obsessive nature more clearly here. Previously he was ruminating for months on the means of murdering his victim, and he presumably had a preoccupation with phrenology based on the story’s beginning, but now he begins to obsess over the possibility of being caught. The narrator then shows the “perverse” impulse’s power in his own life, after giving his broader explanation earlier. Like a real demon, the “Imp” plants a seed in the narrator’s mind, letting him fixate on it and ratcheting up the pressure until he can’t think about anything else. It’s a frightening concept, which serves to convey the nature of the narrator’s madness and how out of control he feels when confronted with his own mind. It’s especially telling that he has
never been able to resist the Imp before.