Why does Della turn pale for a moment as she hears Jim's step on the stair?

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mwestwood eNotes educator| Certified Educator

In this endearing tale of the young, unselfish love of "two foolish children in a flat [apartment]," Della is faced with the dilemma of having very little money with which to buy her husband a Christmas present. Impulsively, she rushes out and sells most of her luxurious hair to Madame Sofronie, who buys ladies' hair to make hairpieces for women. This hair,"rippling and shining like a cascade of brown waters," is one of the two possessions of which "the James Dillingham Youngs....took a mighty pride." Nevertheless, Della willingly sacrifices her prized possession so that she can have enough money to buy her beloved husband a beautiful watch fob. 

After she returns home, she repairs "the ravages made by generosity added to love," curling her short hair into a perky hairdo. But, when she hears Jim's step on the stairs, she is anxious that Jim will be upset when he sees her and no longer find her pretty. "Please, God, make him think I am still pretty," she prays.  When he does enter, Jim stares fixedly at Della with a "peculiar expression" because of the irony of Della's having sold her lovely long hair.