In "A Jury of Her Peers," why did the women choose to hide the evidence of finding the bird?
Let's first discuss what happens when the women find the dead bird. When they find the "pretty" box, Mrs. Hale notices that there is something wrapped up in there, in a piece of silk.
"Oh, Mrs. Peters!" she cried. "It's—"
Mrs. Peters bent closer.
"It's the bird," she whispered.
Then, Mrs. Hale points at the neck of the bird. After Mrs. Peters takes the box away from Mrs. Hale, she concludes that "somebody wrung its neck."
The narrator says then that the women looked at one another, clinging together "in a look of dawning comprehension." This is significant, because it symbolizes the women's first step of becoming complicit in an act that essentially bonds them together on behalf of Minnie Wright.
Each time the narrator uses the words "their eyes met," it becomes evident that the situation is starting to become more clear in the minds of the women, and that they are beginning to understand what took place in the Wright household the night that Minnie snapped and killed her husband. She must have killed him after he killed the one thing that made her happy: her canary.
This being said, the specific answer to your question, on why the women decide to hide the evidence that they find, rather than turn it over to Mrs. Peters's husband and the county attorney, can be found toward the ends of the story when the narrator says that Mrs. Hale looked at the basket . . .
. . . in which was hidden the thing that would make certain the conviction of the other woman—that woman who was not there and yet who had been there with them all through that hour.
Based on this, these are the reasons why they decided to withhold the evidence:
1. Mrs. Hale and Mrs. Peters commiserated with Mrs. Wright. The evidence is that they both feel sorry for her, connect her abuse to personal experiences, and, in the words of the narrator, must have felt that she "had been there with them all through that hour."
2. They know that this evidence will get Minnie convicted. Did Minnie deserve a conviction for snapping, after years of horrible abuse? Maybe she did, legally speaking. However, the women felt a high degree of compassion that led them to hide the evidence, even from their own husbands.
At first, Mrs. Hale and Mrs. Peters are stunned, but soon they find reason to both empathize with their former classmate and friend, Minnie Foster (now Wright.)
As Mrs. Hale and Mrs. Peters talk, they feel guilty about ignoring Minnie; they always found some excuse to put off the visit. Her husband was cold and cruel and made the women feel uncomfortable and unwelcome. But as their conversation continues, the pair recall the Minnie of their youth. Mrs. Peters says, "She -- she was kind of like a bird herself. Real sweet and pretty, but kind of timid and fluttery. How -- she -- did -- change."
As the women watch the investigation, they realize just how isolated and mistreated Minnie had been during her marriage. Then Mrs. Hale and Mrs. Peters discover the dead bird:
" "Somebody wrung its neck," said she, in a voice that was slow and deep.
And then again the eyes of the two women met--this time clung together in a look of dawning comprehension, of growing horror. Mrs. Peters looked from the dead bird to the broken door of the cage. Again their eyes met."
They knew immediately that this was the event that pushed Minnie over the edge.
"She liked the bird," said Martha Hale, low and slowly. "She was going to bury it in that pretty box."
The two women, feeling compassion and comraderie, make the silent decision to hide the evidence.
The play is called "Trifles" and the short story from which the play was written is called "A Jury of Her Peers". In both titles, we get a glimpse of what the play is about--the women are Minnie's peers. They are her equals...NOT the men. The men all throughout the story tease and conjole the women about the small things they concern themselves with--the "trifles" of their lives. For instance, the broken fruit jars, the messy kitchen, Minnie's choice of quilting or knotting the quilt she was working on. They understand her and the life she has lead. Therefore, they know her lonliness and isolation. Without really discussing it, the women have come to an unspoken agreement that they might have done the same thing in Minnie's situation. They concur that Minnie has not done anything for which she should be convicted, and they withhold the evidence.