Wilde uses anthropomorphism throughout the story to create a fairy-tale landscape in which animals and elements of the natural world speak and act like humans—something that invites readers to suspend their disbelief and revisit their assumptions about the differences between humans and nature.
At the very beginning of the story, the Nightingale hears the Student and is moved by his sorrow, saying “here at last is a true lover.” This detail immediately implies that the reader should suspend disbelief and take for granted that the animals in this story are capable of feeling and speaking. In other words, giving animals human qualities gives the story a sense of whimsy and fantasy that forces readers to use their imagination.
The plants in "The Nightingale and the Rose" are also given human qualities. Not only can the trees speak, but they're also given human-like anatomy. When answering the Nightingale’s request for a rose, for example, the trees are described as shaking their “heads,” and when receiving the Nightingale’s sacrifice, the third tree says how the Nightingale’s “life-blood must flow into my veins”. By assigning a human anatomy to the trees, the story portrays the trees as living and breathing creatures, which forges a connection between humans and nature as a whole.
This connection also ironically demonstrates the human characters' coldness. The Student’s oblivious response to the Nightingale’s sacrifice contrasts with the Oak-tree, whose request for one last song and admittance that he “shall feel very lonely” when the Nightingale is gone demonstrates a sentimentality that is absent in the human characters. Indeed, humans in the story prove entirely oblivious to nature's liveliness and inherent value. The Student cannot understand the Nightingale when she speaks or sings to him, and the Professor’s daughter cannot understand the value of the rose. By setting up this contrast (in which nature is sentient while humans are oblivious and unfeeling), Wilde subverts expectations, forcing readers to engage more critically with the story. This choice also arguably comments on the unfeeling rationalism and cold industrialism of the modern age.