Relationships between humans and nonhuman animals and the differences between the two are central themes in the work. One recurring element is the scientific study of nonhuman animals and interspecies relationships versus the intangible, emotional elements of these relationships. Rosemary’s father views Rosemary and Fern through a strictly scientific lens, so averse to the idea of anthropomorphism that he leaves little room for findings that cannot be put into an experiment and proven. Conversely, the rest of the Cooke family opens their minds to potentially anthropomorphic ideas. For example, young Rosemary believes that she and her sister can communicate telepathically. When Vince and the graduate students focus more on Fern’s behavior than Rosemary’s pain, Rosemary believes her sister empathizes with her, sharing an example of a time when Fern shared a red poker chip with Rosemary in what Rosemary believes is an apology. In believing that nonhuman animals experience emotions just like to humans do, Rosemary is able to have empathy for animals, seeing herself in them and them in her. Once animals are recognized as beautiful and intelligent, it becomes harder to objectify and abuse them.

As an adult, Rosemary connects her physical and emotional experiences with those her sister may be having.