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.
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.