Why did Faulkner use all of the images of metal and stiffness in referring to Abner Snopes?
Faulkner's use of metal imagery and stiffness is reflective of how Abner Snopes constructs his reality. The world in which Snopes lives is hard, absolute, and little is present in way of contextual flexibility. Even when he reprimands Sarty, one can see this rigidity and sense of absolutism: "You're getting to be a man. You got to learn. You got to learn to stick to your own blood or you ain't going to have any blood to stick to you." The world in which Snopes lives operates by absolute moral and ethical codes. It is a strict adherence reflected in Abner's identity: "harsh like tin and without heat like tin.” Flexibility and understanding that moves one towards ambiguity is absent. It is in this manner that he is able to function in an authoritarian manner. It is a position that shows his disdain towards a world against which he holds disdain. This metallic rigidity is how he causes challenges and grief to those who live with him. For Faulkner, being able to use stiffness and imagery that reflects inflexibility are ways to communicate this sense of control and authority with which Abner appropriates the world and his place in it.
Faulkner also uses such a rigid manner of description for Abner to show how disjointed he is in the world. This becomes clear when Faulkner describes how Abner would rather walk with his stiffness and absolute totality as opposed to avoid stepping in droppings:
Watching him, the boy remarked the absolutely undeviating course which his father held and saw the stiff foot come squarely down in a pile of fresh droppings where a horse had stood in the drive and which his father could have avoided by a simple change of stride.
Abner's characterization is that he does not show contingency to acquiesce to a "simple change of stride." He walks with a rigidity that reflects how he functions in the world. He is unyielding. When he confronts anyone who he perceives as a threat, he does so without any reflection and recompense. His rigidity and stiffness is an assertion of power.
Yet, Faulkner shows that Abner lacks any real power in the world. The act of barn burning is the only way in which Abner is able to demonstrate strength. For Abner, the rigidity and totality in the world is reflective of how he views fire in burning barns: "The element of fire spoke to the mainspring of his father's being […] as the one weapon for the preservation of integrity […], and hence to be regarded with respect and used with discretion." Abner appropriates the world in a strict manner, without any ambiguity. It is for this reason that he causes destruction to others, most notably his family.
Faulkner has to construct Abner in an external manner to illuminate his internal subjectivity. In describing him in terms of stiffness, rigidity, and metallic elements, Faulkner is able to evoke how his external mannerisms matches an internal disposition towards being in the world.