Tedious speech
In the following quote, Dahl uses a simile to describe how someone speaks in a tedious manner: "He made a mournful monotonous song with his words, as a clergyman does when he is paid to recite prayers in public."
Coco Islands
In one passage of the book, Dahl uses a simile to describe the Coco Islands, which "lie in solitary splendor in the middle of the Pacific Ocean like a handful of precious stones." As such, he uses the simile to make them seem beautiful and mystical.
Humanity metaphor
In this novel, humanity ultimately destroys itself after years of warfare. This is a metaphor for the self-destructive tendencies of humanity.
Living together in peace
Ultimately, if only humanity and the gremlins had put peace before warfare, they would still remain at the end of the novel. As such, this is a metaphor for the fact that people would be much better off living together in peace than fighting.
Gremlin metaphor
The gremlins in this novel are a metaphor for people who are consumed by bitterness and are set on getting revenge. In the end, the gremlins don't win as they find they cannot actually live without humanity.