Hemingway has the man and the girl engage with the beaded curtain at the entrance to the bar several times during the story, forming a motif. Given Hemingway’s minimalist use of language, whenever he takes time to describe an element of the setting, it suggests that said element holds broader symbolic or thematic importance. He introduces the curtain in the following way at the beginning of the story:
Close against the side of the station there was the warm shadow of the building and a curtain, made of strings of bamboo beads, hung across the open door into the bar, to keep out flies.
This description helps readers picture the “strings of bamboo beads” and also understand its role as a force that keeps things out (in this case, flies). From the start, the curtain seems to represent a barrier against things that are pesky or unwanted, which is perhaps why, at the end of the story, the man goes inside the bar to join the other “reasonable” people, leaving the girl outside and on her own.
Scholars are not in full agreement about the significance of the curtain, however, as its purpose seems to shift over the course of the story. For example, it is right after “the warm wind blew the bead curtain against the table” that the man describes an abortion as a procedure that “let[s] the air in.” Here, the curtain almost seems to be on his side, with the wind inspiring him to approach his argument in a new way. And, later, the girl takes “hold of two of the strings of beads” while asking the man if he thinks they’ll really “be all right and be happy” if she gets an abortion. Here, the curtain almost acts as a rosary that the girl uses while offering this sort of prayer.
Because of Hemingway’s intentionally minimalist use of language, it’s difficult to determine the precise purpose of the beaded curtain motif, but it’s clear that the curtain's presence is tied to the challenging choice the couple has to make over whether the girl gets an abortion or not.