There are several motifs and symbols in the playTriflesthat acquire major significance when looked in context.
Proximity- This particular motif is not in plain sight, but then you realize that males and females are consistently separated or at a far range of proximity, both physically and seemingly socially, throughout the play. The men are familiar to each other and joke around. The women maintain their distance and call each other by last names. Yet, at the obvious realization of what really happened at Minnie Wright made the woman come closer as in joining Minnie's cause.
Telephone- The party-line telephone that John Wright possessed at a great expense would have served to connect Minnie to the outside world. Ironically, she was cut off from the rest of the world and isolated against her will. She, like the phone, were symbols of John's macho need to be the alpha whom others need. The fact that John keeps Minnie isolated makes him all the more guilty of his own death. He created Minnie's inner "monster".
Stitching on the quilt/ Incomplete tasks-In "Women's Work--Trifles? The Skill and Insights of Playwright Susan Glaspell", *Smith (1982) argues
The incomplete tasks in Minnie's kitchen argue that she acted very soon after provocation, John's strangling of the bird (p.182)
Whether she snapped or not, it is clear that the pattern of provocation had seared in Minnie's brain long enough, and that the potential here is that she had switched to a survival mode of life where, at the lowest and most anxious point, she has to end the life of the predator.
The bird - Throughout history, the arts have always given birds a semi-ethereal role where they serve as messengers, carriers, or even the very essence of innocence. Similarly, the bird being killed is synonymous with John literally killing the last drop of innocence in her soul, and also literally, making her guilty of murder (regardless of the circumstances). Therefore, all that had to happen was for John to commit one more act, abuse Minnie one more time, or try one more act of power, for Minnie to finally take control in one way or another.
Along with these contextual indicators of meaning, the pun in the title "Trifles" serves as an ironic fact: all of these elements mentioned could have helped the county attorney to build his case. Yet, the prevalent feeling that women are second class citizens, and that their attention to details is a waste of time is precisely what leads the case to go awry. All the women have to do is hide the key evidence, those very "trifles", and save Minnie Wright.
*Source: Smith, Beverly A. "Women's Work--Trifles? The Skill and Insights of Playwright Susan Glaspell." International Journal of Women's Studies 5 (March 1982): 172-84.