The engineer and the mage
Obviously, Cocoa's life has been magical since she was young. For instance, her mother seems to be able to practice witchcraft, and Cocoa even bears a real hex from a malicious witch named Ruby. On the other hand, George is a modern man, and an engineer of all things. This is an ironic, star-crossed pair.
The good and bad witch
Another ironic set of opposites occurs in the complementary characters Mama Day (the "good witch") and Ruby (the "evil witch"). As a pair, the two represent the dual nature of the unknown (especially to George). Mama Day represents the universe's ability to help people to succeed, and Ruby represents the reality of death, the danger of the unknown, and even hatred and malice.
The ironic failure
There is dramatic irony in the finale of the story when George basically kills his wife. The reader, already clued into the novel's allowance for magic and the supernatural, knows that if George resorts to his materialistic default mode, he will seriously harm his wife, and in the end, she dies. It is also ironic for the novel to end with a failure, since he seemed to be making progress.
The good spell
Mama Day curses George in the novel, and Ruby curses Cocoa. This is ironic, because George, who doesn't believe in magic, is captivated by a magical spell almost the whole time. When he returns to Willow Springs, he believes he is still autonomous, he is actually part of a magical landscape. His sureness in science means blindness in the unknown terrain.
The bridge catastrophe
Let's say that George realizes Cocoa is sick, and he takes her to a doctor. Maybe she lives, or maybe she dies, but in either case, George remains able to use science instead of magic. Therefore, as if by design, a random hurricane destroys the bridge between the safe, known world, and the mystic unknown of Willow Springs. George is trapped.
