In Edgar Allan Poe's "The System of Doctor Tarr and Professor Fether," the narrator expresses his wariness while conversing with a young woman, suspecting her mental soundness. The narrator's observations suggest an unsettling brilliance in her eyes, hinting at her potential instability or madness. This describes a tension in their interaction, as he navigates the uncertainty of her state of mind.

The narrator's cautious demeanor reflects a broader theme of how appearances can deceive and provoke doubt. The young lady's enigmatic nature captivates the narrator, yet it also instills a sense of fear regarding the unpredictability of her thoughts and actions. This duality underscores the complexities of human behavior and perception, illustrating Poe's exploration of sanity and madness.