In Kenneth Oppel's Half Brother, the themes of Communication and Understanding are closely tied to the story, exploring the complex and tricky issues of human-animal relationships. Through the special bond between Ben and Zan, the novel shows how communication shapes relationships and how humans see intelligence and empathy. It raises important questions about how people treat animals and each other and what it means to understand another being.

For Zan, communication occurs almost entirely through American Sign Language (ASL), body language, and tantrums. While Zan can communicate his wants and needs with his caretakers, they do not always listen to him, even when they understand. Frequently, Zan expresses his desires only to have those around him ignore him. Further complicating others' understanding of Zan is his lack of effective communication with other chimpanzees. When Zan moves to Helson's ranch, he tries to communicate via sign language, but the other chimps do not understand him. Zan has no other way to communicate, as no one ever taught him how to communicate like a chimpanzee. This language barrier leads to difficulties integrating with other chimpanzees, as they do not understand him.

Ben is the only person who genuinely understands Zan.