The snake in the woodpile
When the snake slithers away to safety, that means bad news for the family. They don't know whether they will survive or not, because if they sleep, the snake could reemerge and strike them in their sleep. The snake in the woodpile is the threat of danger that looms close to home, but it is concealed by the woodpile, which turns the threat into a dramatic irony. The combination of threat and the unknown makes the family incredibly paranoid, as their minds and bodies go into survival mode, constantly hoping to detect threats before it is too late.
The symbolic apples
The apple trees around the home were originally a symbol of life, like the trees in the garden of Eden (another important human versus snake story). However, what was once a symbol for life and sustenance now carries another looming meaning; because the trees are all starved of rain from the recent drought, they are easily flammable, and they are surrounded by dry brush. A rogue spark anywhere nearby in the bush could mean inescapable death by fire. The apple tree represents death by fire.
The rain conundrum
The wife has a relationship to nature that is difficult and surprising. Her conundrum is whether it will rain, which will lead to apples in her orchard and less competition in the bush (so hopefully less snakes will bother her family). But, if it does not rain, the threat of wildfire gets daily worsened. This dramatic irony leads her mind into a chronic state of fight-or-flight. Should she fight through this drought to a better future, or should she admit that the bush is not the place for her family, and flee to some unknown future.
The hero depression
The Wife's defining features are the very aspects of her character that she doubts the most. Because she is constantly trying to save her family from harm, she takes each death as a reflection of her own worthlessness and failure, but in reality, the death is a symbol for itself. Death is an undefeatable foe for all humans. Ironically, her heroic nature, her willingness to lay her life down for others and to protect others, makes her feel a depression because she is not powerful enough to defeat an undefeatable enemy.
The self-sacrifice
It is ironic in the first place that anyone should want to die to save another person's life. That is the irony of her maternal love. The kids struggle to understand how much she loves them, because they are still growing. They don't see that the mother is honestly terrified of the snake. When Tommy tries to help her in a battle against the poisonous serpent, she refuses him—it is for his absolute safety that she even fights the snake. It isn't just to defeat snakes—it is to save her children from danger, because she loves them.
