After Mr. Roe tells Helen that he killed several Mexican bandits with a bottle filled with small rocks, she fixates on stones. From this point on, Treadwell’s treatment of stones takes on a metaphorical aspect, in which stones represent Helen’s burdensome responsibility as a wife and mother. Indeed, Helen tells George at one point that she feels like she’s “drowning” with stones around her neck, though they’re merely sitting in the living room on a normal night of their domestic lives. Helen then starts hearing voices that chant and echo Mr. Roe’s words; “Stones—stones—precious stones—millstones—stones—stones—millstones,” the voices say. The use of the word “millstone” is important, as a millstone (originally a large stone used for grinding grain) is normally understood as a symbol of heavy responsibility that a person wears around their neck. This image also comes from the Bible, in which Jesus tells his disciples that wicked people who cause “these little ones to stumble” should be thrown into the sea with millstones around their necks. As such, Treadwell evokes both the idea of responsibility and the idea of death and punishment, two notions that have strong emotional importance to Helen. Therefore, when these voices chant about stones, Helen is simultaneously reminded of Mr. Roe, of her supposed responsibility to make George happy, and of her own feeling of sinking under the pressure of her domestic life. With these thoughts whirling through her mind, she kills George with the same weapon Mr. Roe used on his attackers: a bottle filled with stones.
In addition to the symbolic significance of stones outlined above (responsibility and death), Helen’s choice of weapon also indicates her distrust of the mechanical world. Opting for to use a wine bottle filled with rocks, she chooses the most rudimentary possible way to murder George, thereby lending a sense of elemental simplicity to the already thematically-charged presence of stones in Machinal.