Probably one of the most profound examples of ambiguity in Lord of the Flies occurs early on in the novel when the boy with the mulberry birthmark disappears. In Chapter Two, "Fire on the Mountain," the boys rush to build a signal fire after Ralph mentions the idea in the assembly. Only later on after Piggy mockingly points out that the fire is completely out of control, does he realize that the little boy with the birthmark is missing.
The reader never receives a clear answer on his fate, but does Golding provide evidence to suggest his death in the form of the ominous drumroll of the fire down the mountain. Golding's use of ambiguity, particularly in the little boy's death, informs the reader that the other boys' time on the island certainly will not be all fun and games, and not knowing what happened to the little boy leaves the reader with the same sense of anxiety felt by the characters in the story.
An example could be how the author does not specifically say who is speaking in the dialogue and the reader gets confused.