After Captain Beatty leaves, Montag shows Mildred his hidden book collection inside the ventilator. He encourages her to begin reading in hopes of learning important information that might alter the trajectory of their lives. While Montag is reading, the couple hears a faint scratching at the door. Mildred responds to the sound by thrusting her back to the wall and wonders why the "door-voice" did not inform them that someone was at their door. Montag comments that he "shut it off" and instructs his wife to remain still until the person or creature leaves. Montag anticipated that either Captain Beatty or someone associated with the firemen would return to his home, and he did not want to be interrupted while reading, which is why he shut off the "door-voice."
Montag and Mildred proceed to hear "a slow, probing sniff" underneath the door followed by an "exhalation of electric steam." Montag recognizes that it is the Mechanical Hound outside his door, which Captain Beatty purposely sent to his home as a warning. Montag understands that his life and freedom are in jeopardy if Mildred opens the door. However, he dismisses the Mechanical Hound, instructs Mildred to not open the door, and continues to read.