One of the major themes in Triflesis the social tradition of gender roles. The men walk into the house, assuming command of the investigation while the women (who are never referred to by their first names) appear meek and inconsequential. However, it is the women who do the real detective work while the men look for hard physical evidence, ignoring the subtle implications of the state of the house and the relationship between Mr. and Mrs. Wright.
Two symbols are the bird cage and the dead canary. Mrs. Hale supposes that John Wright killed the bird. The cage is symbolic of Mrs. Wright's imprisoned existence with Mr. Wright. Mrs. Hale notes that Mrs. Wright sang like the bird. "She used to sing. he killed that, too." Mrs. Hale implies that Mr. Wright killed Mrs. Wright's, Minnie's, spirit.
It is clear that the women are comparing the bird to Mrs. Wright. Each sang perhaps to express themselves in general and/or to express desire to escape from their respective cages.