How does the author use foreshadowing in The Elephant Man?

In Scene Four, Ross finds himself on the receiving end of Merrick's vengeful anger, for his part in robbing him of his income. Meanwhile, the appearance of the pinheads, their fumbling of the song and the way they are abused foreshadow their appearance at the end of the play; when they sing perfectly and behave with grace and gentleness, almost as though they are angels.