He realises that all the firemen look alike
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They and their charcoal hair and soot-coloured brows and bluish-ash-smeared cheeks where they had shaven close; but their heritage showed. Montag started up, his mouth opened. Had he ever seen a fireman that didn't have black hair, black brows, a fiery face, and a blue-steel shaved but unshaved look? These men were all mirror-images of himself! Were all firemen picked then for their looks as well as their proclivities?
Fahrenheit 451, pg. 15