Faulkner's macabre surprise ending contains not one but two shocking epiphanies:  Not only do the men discover the rotting corpse of Homer Barron in the bed, but in the indentation of the second pillow rests a single strand of iron-gray hair. We can assume that it is Emily's hair and indicates that Emily has been sleeping alongside the corpse for many years, since her hair was not yet gray while she and Homer were courting. Her hair turned gray over time, and consequently the gray strand must have been a recent remnant.

What is the significance of the iron-gray hair found on the second pillow?
Ah, a fine detail. That hair indicates that Miss Emily has been sleeping there. On that second pillow. Next to a corpse! Aiee!