Montag shook his head. He looked at a blank wall. The girl's face was there, really quite beautiful in memory: astonishing, in fact. She had a very thin face like the dial of a small clock seen faintly in a dark room in the middle of a night when you waken to see the time and see the clock telling you the hour and the minute and the second, with a white silence and a glowing, all certainty and knowing what it has to tell of the night passing swiftly on toward further darknesses but moving also toward a new sun.
"What?" asked Montag of that other self, the subconscious idiot that ran babbling at times, quite independent of will, habit, and conscience.
He glanced back at the wall. How like a mirror, too, her face. Impossible; for how many people did you know that refracted your own light to you? People were more often - he searched for a simile, found one in his work-torches, blazing away until they whiffed out. How rarely did other people's faces take of you and throw back to you your own expression, your own innermost trembling thought?
What incredible power of identification the girl had; she was like the eager watcher of a marionette show, anticipating each flicker of an eyelid, each gesture of his hand, each flick of a finger, the moment before it began. How long had they walked together? Three minutes? Five? Yet how large that time seemed now. How immense a figure she was on the stage before him; what a shadow she threw on the wall with her slender body! He felt that if his eye itched, she might blink. And if the muscles of his jaws stretched imperceptibly, she would yawn long before he would.
resembles Plato's Allegory of the Cave:
Plato has Socrates describe a group of people who have lived chained to the wall of a cave all of their lives, facing a blank wall. The people watch shadows projected on the wall from objects passing in front of a fire behind them, and give names to these shadows. The shadows are the prisoners' reality. Socrates explains how the philosopher is like a prisoner who is freed from the cave and comes to understand that the shadows on the wall are not reality at all, for he can perceive the true form of reality rather than the manufactured reality that is the shadows seen by the prisoners. The inmates of this place do not even desire to leave their prison, for they know no better life. The prisoners manage to break their bonds one day, and discover that their reality was not what they thought it was. They discovered the sun, which Plato uses as an analogy for the fire that man cannot see behind.
Other reference to the same allegory could be Mildred's wall-TV show. She is basically living her life looking at and communicating with TV characters which are projected on the wall, which replaces the reality for her.