"As pygmies may threaten a giant, so those angry fists were directed against the sky fifty kilometers above his head" (7) (Simile)
This simile emphasizes the smallness of humanity, as a crowd of people raises their fists in protest against the Overlord fleet.
"This was another of those restless nights when his brain went on turning like a machine whose governor had failed" (20) (Simile)
This simile describes the turbulence of Stormgren's mind when he tries to sleep; he struggles with his relationship to humanity on the one hand, and to the Overlords on the other hand.
"Imagine that every man's mind is an island, surrounded by ocean. Each seems isolated, yet in reality all are linked by the bedrock from which they spring. If the oceans were to vanish, that would be the end of the islands. They would all be part of one continent, but their individuality would have gone. Telepathy, as you have called it, is something like this" (151) (Metaphor)
Rashaverak uses this analogy to try to explain telepathy to George. More generally, this is a way to metaphorically understand the connection between Jean and Jeff, and the Children's evolution.
"Though the submarine canyon had been formed geological ages ago, the tortured rocks had never reconciled themselves to their new positions. Countless times the strata bad creaked and shifted, as the unimaginable weight of water disturbed their precarious equilibrium. They were ready to move again." (145) (Metaphor)
Clarke uses the metaphor of the evolutionary processes of the islands of New Athens and New Sparta to give insight into the evolution that is slowly happening in Jeffrey: like the rocks of the canyon, he will soon be "ready to move again."