How does the author use metaphor in the novel, Ms. Bixby’s Last Day?

Anderson uses poisonous snakes as a metaphor for cancer. When Steve learns about poisonous snakes, he shares the information with Ms. Bixby. She later asks him to search for the moral context of the information when she reveals her diagnosis, which he explains as that just because something can happen, does not mean it will. Just because cancer can kill someone, does not mean it will.