William Golding uses figurative language throughout Lord of the Flies. It is a highly symbolic novel, so it is not surprising to find examples of imagery used as foreshadowing throughout the work.
One significant use of imagery in the novel happens in chapter one after Ralph has blown the conch and the boys have started to gather. Suddenly everything grows quiet because they see something in the distance.
Within the diamond haze of the beach something dark was fumbling along. Ralph saw it ﬁrst, and watched till the intentness of his gaze drew all eyes that way. Then the creature stepped from mirage on to clear sand, and they saw that the darkness was not all shadow but mostly clothing. The creature was a party of boys, marching approximately in step in two parallel lines and dressed in strangely eccentric clothing.
Obviously what the boys see is the choir, but the description suggests it is some kind of beast (dark, fumbling, creature) rather than a group of black-cloaked choirboys marching in some semblance of unity. This is a clear foreshadowing of all the "beast" talk and action on the island.
Another example of imagery can be found in chapter two after the boys have lit what was supposed to have been a small signal fire. Instead they create a conflagration:
Small ﬂames stirred at the trunk of a tree and crawled away through leaves and brushwood, dividing and increasing. One patch touched a tree trunk and scrambled up like a bright squirrel. The smoke increased, sifted, rolled outwards. The squirrel leapt on the wings of the wind and clung to another standing tree, eating downwards. Beneath the dark canopy of leaves and smoke the ﬁre laid hold on the forest and began to gnaw. Acres of black and yellow smoke rolled steadily toward the sea. At the sight of the ﬂames and the irresistible course of the ﬁre, the boys broke into shrill, excited cheering. The ﬂames, as though they were a kind of wild life, crept as a jaguar creeps on its belly toward a line of birch-like saplings that ﬂedged an outcrop of the pink rock. They ﬂapped at the ﬁrst of the trees, and the branches grew a brief foliage of ﬁre. The heart of ﬂame leapt nimbly across the gap between the trees and then went swinging and ﬂaring along the whole row of them. Beneath the capering boys a quarter of a mile square of forest was savage with smoke and ﬂame. The separate noises of the ﬁre merged into a drum-roll that seemed to shake the mountain.
This passage is replete with figurative language, as the fire is personified first as a squirrel and then, as it grows, as a jaguar; finally it is a place "savage with smoke and flame." In every way, this is a foreshadowing both of the savagery to come as well as the next fire which will also become a conflagration. Even the final line, an ominous drum-roll that shakes the mountain, is an indication of the savagery and destruction which is to come.
Golding tried to warn with his imagery about what is to come, just as he wrote his novel as a warning about the true nature of man when the restraints of civilization are removed.