Although Prendick does not seem to be a liar, he is an unreliable narrator. For example, in Chapter 10, he describes waking up in Moreau's house to the sound of human screams:
Then I recalled the expression of [Montgomery's] face the previous night, and with that the memory of all I had experienced reconstructed itself before me. Even as that fear returned to me came a cry from within. But this time it was not the cry of the puma. [...]
There was no mistake this time in the quality of the dim broken sounds, no doubt at all of their source; for it was groaning, broken by sobs and gasps of anguish. It was no brute this time. It was a human being in torment!
As it turns out, it is the puma screaming after all. By the time Prendick is writing his account of Doctor Moreau's island, he knows he was wrong. He misleads the reader here because of his commitment to report events not as they objectively happened, but rather as he experienced them. He declares outright that "[i]t was a human being in torment!" despite knowing otherwise because this declaration conveys the certainty he felt at the time that he was hearing a human's "sobs and gasps of anguish."
Prendick's faithful report of his experience, rather than the objective truth, contributes to the horror of the novel. He is allowing the reader to imagine viscerally, not just intellectually, what it was like to be on the island. After reading his account, the reader should be left not only with the facts of the situation but also with some of the emotional weight Prendick has carried since his time there. Prendick forces the reader to process the idea that the puma's cries are human because he had to process this same idea. By holding back the truth, Prendick manipulates the reader into a state of paranoia, similar to the paranoia he experiences when he returns to mainstream society at the end of the novel.
Prendick's genuine belief that he is hearing human screams emphasizes the central uncertainty of the novel: is there a discernible difference between humans and animals? Prendick feels genuine human sympathy for a creature who turns out to be an animal. On the one hand, the puma is not human (at least not at this point in the vivisection process). On the other hand, Prendick's mistake reveals that it is difficult for the human senses to tell at what point a creature becomes human. This uncertainty about the boundary between human and non-human cropped up in discourse around scientific racism as well as around vivisection. During this period, many mainstream scientists made the racist claim that Black people were a less evolved, animalistic form of human than white people. Wells is conveying as much unease about this ideology as he is about the ethical limits of vivisection.
In Chapter 22, Prendick describes his return to England after he escapes from the island and is rescued at sea. He uses a simile to describe a "delusion" he has about the people there:
I would go out into the streets to fight with my delusion, and prowling women would mew after me, furtive craving men glance jealously at me, weary pale workers go coughing by me, with tired eyes and eager paces like wounded deer dripping blood, old people, bent and dull, pass murmuring to themselves, and all unheeding a ragged tail of gibing children.
Prendick's time on the island essentially turns him into a misanthrope. He does not believe that the people in England are really going to start behaving like bloodthirsty animals, but he has such a deep paranoia about it that he can hardly bear to live among them. Here, he compares the working class to "wounded deer dripping blood," presumably because they are being preyed upon by the people and systems exploiting them. Just as a predator in the woods might attack a deer without concern for its quality of life if it survives, society leaves the working class to struggle along on the brink of death. Although Prendick describes fighting his "delusion," this simile suggests that he might not be as delusional as he thinks. There were some protections for laborers in England by the time Wells wrote this book, but a great many protections had yet to be passed. The working class really were being preyed upon, much like prey animals in nature. Prendick is once again revealing himself to be an unreliable narrator, but this time it is because he doesn't see how right he is about the world.
Prendick's time on the island traumatizes him, but it also allows him to see English society as the wild and vicious ecosystem it is. It is significant especially that Wells draws attention to the working class given his interest in this novel and elsewhere (especially The Time Machine) with class uprisings. Wells had the sense that the working class was going to rebel against the ruling class sooner or later unless they were given more social safety nets. The political history of the 20th century is extremely complex, but Wells was correct that wealth disparity would lead to major conflict in the decades to come.
