The one-act play Trifles by Susan Glaspell concerns a murder investigation after the death of John Wright, a local farmer. Wright's wife Minnie has been arrested for the murder. The investigation takes place at Wright's farmhouse. A farmer named Lewis Hale, Sheriff Peters, and the county attorney George Henderson are looking for clues, and they are accompanied by Mrs. Hale and Mrs. Peters. The men leave the women in the kitchen while they go about the house. They are obviously being condescending and consider the women incapable of offering much assistance. However, the women uncover clues to the murder that they eventually decide not to share with the men. The theme of the play concerns the gender divide between the men and the women and how it demeans the women and hinders the investigation.

Besides the birdcage, there are several important symbols in the play. For instance, the party telephone line that Mr. Hale suggested to John Wright symbolizes connection with the community. One of the forms of abuse that Mr. Wright subjected his wife to was isolation from the larger community around them. The phone would have connected her with her neighbors, but Mr. Wright was intent on depriving her of that.

The jars of preserves, most of which are broken, are symbolic of the work that the women do on their farms. They are expected to fulfill their roles as housekeepers while the men do the outside work and govern the community. Despite being demeaned in this way, the women do their best to perform their work diligently and well, as evidenced by Minnie Wright's concerns about her fruit, which Mr. Hale dismisses as trifles. Mrs. Hale is pleased when she finds an intact jar of cherries, knowing it will encourage Mrs. Wright. Similarly, the apron that Mrs. Wright asks for, even though she is in jail, is symbolic of her work in the household defining her identity.

The two women find a quilt that Mrs. Wright had been working on. It shows mostly regular work, and then the stitching becomes erratic. This is symbolic of Mrs. Wright's confused state of mind. In sympathy, Mrs. Hale repairs the stitching.

One of the most important symbols is the canary with the broken neck. When the bird was alive and singing, it would have represented life, freedom, and joy for Mrs. Wright. However, the broken neck symbolizes the extent of the cruelty and abuse of Mr. Wright. The canary is the vital clue that might have proved Mrs. Wright's guilt. The choice of the women to withhold it from the men shows their sympathy for Mrs. Wright.

In Susan Glaspell's Trifles, besides the bird-cage, the canary, the rope, the red box, the erratically sewn quilting, and the broken fruit jars are key symbols that relate to Mrs. Minnie Foster Wright.

• The canary

The little yellow songbird is representative of Minnie Foster, once a bright young woman of the town who was in the church choir where she loved to sing, just as the little bird sings in her lonesome and isolate farm house. While Minnie owns the bird, she is able to experience some joy as she delights in its song. However, her husband's silencing of this one voice of song terminates the music, long a joy for Mrs. Wright, causing her to feel desolate. In fact, the strangled songbird is a "symbolic analogue" (http://www.enotes.com/topics/trifles/critical-essays/essays-criticism) of Minnie's desperate loneliness. 

MRS. HALE. ...she [Minnie Foster Wright] was kind of like a bird herself--real sweet and pretty, but kind of timid and--fluttery.

• The rope

The rope with which Mrs. Wright retaliates in similar fashion against her husband by strangling him is an act symbolic of the unyielding emotional strangulation imposed upon Minnie Wright by her cold and heartless husband. 

• The red box

Red is a color that connotes passion, blood, life, and love. The pretty red box in which Minnie lays her little dead canary symbolizes the emotions that this bird has long aroused in Minnie, emotions stifled by her overbearing husband. The box also represents the love with which Minnie has endowed her little pet.

• The missed stitches of the quilt

The erratic stitches in Minnie's quilt represent Minnie's emotional state after the little songbird is killed. When Mrs. Hale sees this stitching, she points it out to Mrs. Peters:

MRS. HALE. ....look at the sewing! All the rest of it has been so nice and even. And look at this! It's all over the place! Why, it looks as if she didn't know what she was about!.....I'll just finish up this end. (Suddenly stopping and leaning forward) What do you suppose she was so nervous about?

These missed stitches represent, or symbolize, the state of mind of the desperate Mrs. Wright.

• The broken fruit jars

The fruit jars that have frozen and broken from the low temperatures represent a great amount of diligent work that Mrs. Wright has done. After all her years of cooking and cleaning and sewing for an estranged and insensitive husband, the fruit jars represent the woman who married John Wright, a man who was subjugated and repressed to the point that she broke, like the jars, and her "fruits" of musical talent and artistry have been wasted in the barren home in which she lives.

The bird itself is the main symbol in Trifles. Just as Mr. Wright literally choked the life out of Minnie Wright, he also destroyed his wife's spirit.  Mrs. Hale mentions that Minnie "used to wear pretty clothes and be lively . . . one of the towns girls singing in the choir."  After marrying Mr. Wright, she lost her voice--the ability to be cheerful--and, more importantly, she lost who she was.  The death of the bird symbolizes the death of Minnie Foster--who she was before marrying Mr. Wright.

Likewise, the rope (noose) which Minnie uses to kill her husband symbolizes the motif of "choking out someone's life."

In regards to symbolism, the quilt pieces also play a major role.  The women's reaction to the poorly sewn quilt piece demonstrates the difference between men's and women's perception.  The women realize that the piece is significant, but to the men, the sewing represents the trifles that usually occupy the minds of women.  The County Attorney asks the women in a tongue-in-cheek manner, "Well, ladies, have you decided whether she was going to quilt it or knot it?" Their answer of "knot it" illustrates the secret knowledge they have gleaned from paying attention to detail, and it also hints the manner in which Minnie murdered her husband.