The mood of the novel is predominantly anxious. For instance, in Chapter 8, Prendick coaxes the reader into an anxious mood by describing the experience of hearing the puma screaming in the next room:
I found myself that the cries were singularly irritating, and they grew in depth and intensity as the afternoon wore on. They were painful at first, but their constant resurgence at last altogether upset my balance. I flung aside a crib of Horace I had been reading, and began to clench my fists, to bite my lips, and pace the room.
Presently I got to stopping my ears with my fingers.
Although Prendick is hearing the puma's screams, and although the reader can imagine the puma's screams, the focus of this passage is on the way Prendick experiences the screams in his own body. He feels irritation, pain, a sense of imbalance, a lack of concentration, and tension that manifests in clenched fists, bitten lips, and pacing. Finally, he is compelled to do what he can (stopping his ears with his fingers) to tune out the sound.
By focusing on his own embodied experience of anxiety, the narrator creates a reading experience that mirrors his own experience on the island. It is important for Wells that the reader feel the anxious curiosity and revulsion toward the Beast Folk that Prendick feels. As Prendick goes on to write in this same passage:
Yet had I known such pain was in the next room, and had it been dumb, I believe—I have thought since—I could have stood it well enough. It is when suffering finds a voice and sets our nerves quivering that this pity comes troubling us.
Simply knowing about the Beast Folk and about Prendick's horrifying experience on the island is not enough to throw readers off balance. If Wells wants the reader to be moved by his novel, he needs to "set [the reader's] nerves quivering." The written form of a novel makes it difficult to make the reader actually hear the "voice" of the puma, so Wells instead has Prendick describe the effect the voice has on him. Prendick's "quivering nerves" thus become a weather vane that clues the reader in to how "troubled" they should feel.
By unsettling the reader about the island, Wells incites anxiety about broader societal issues as well. By the end of the novel, Prendick has returned to England but finds it "troubling" to live among people whom he does not trust not to start behaving like Moreau and the Beast Folk. The reader, already trained to share in Prendick's anxiety, is left feeling likewise paranoid about the instability of society.
