How does Jim react when he first sees Della after she has cut her hair in O. Henry's short story "The Gift of the Magi"?
When Jim walks through the door, he possesses an unreadable expression that utterly terrifies his tremulous wife.
It was not anger, nor surprise, nor disapproval, nor horror, nor any of the sentiments that she had been prepared for. He simply stared as her fixedly with that peculiar expression on his face.
Della quickly explains that she cut and sold her hair because she wanted so badly to buy him something nice for Christmas. She also assures him that her how grows very fast and that she's bought him a really lovely gift with the money she got for her hair.
"You've cut off your hair?" asked Jim, laboriously, as if he had not arrived at that patent fact yet even after the hardest mental labor [....]. Jim looked around the room curiously. "You say your hair is gone?" he said, with an air almost of idiocy.
Jim's initial, and somewhat lengthy, response seems to be disbelief. After all, the narrator tells us that he's neither mad, nor shocked, nor disapproving, nor horrified. He speaks "laboriously" and slowly, as though he has some deficiency of understanding, almost like an "idiot." In other words, he seems, simply, to be unable to believe the supreme irony of what has happened. After all, he knows before Della does that they each have done the same thing—sold their most valuable possessions to buy something nice for the other—and he initial disbelieving response does fade quickly.
Just before Jim arrives home from work Della says a little prayer: "Please God, make him think I am still pretty." Della has just sold her beautiful hair (her prized possession) in order to buy a watch chain for Jim's watch (his most prized possession).
Della is apprehensive about Jim's reaction to her new look. When he arrives home, O. Henry uses a simile to describe the look on Jim's face: "Jim stopped inside the door, as immovable as a setter at the scent of quail." O. Henry further remarks that Jim was neither "surprised," "horrified" or in a state of "disapproval." Della's appearance simply puts Jim into a "trance." Two things must have gone through his head. First, his wife has cut off her beautiful hair and, second, the new "tortoise shell" combs he has bought are not as appropriate as they once were. Nevertheless, he still loves her as he remarks,
"Don't make any mistake, Dell," he said, "about me. I don't think there's anything in the way of a haircut or a shave or a shampoo that could make me like my girl any less. But, if you'll unwrap that package you may see why you had me going at first."
Jim's reaction has more to do with the revelation about the combs than any positive or negative reaction to Della's hair. The point of the story is that this couple have overwhelming love for each other that goes beyond physical beauty. They are willing to sacrifice their most prized possessions to demonstrate that love.