How does the author use foreshadowing in Wyrd Sisters?

The lakeside encounter between Magrat and the Fool marks the first fracture in the Fool's thus far solid duty to Lord Felmet. Though he was ordered not to divulge information to the witches, the Fool nevertheless does so. What's more, he also willingly provides intelligence concerning the play, its intent, and how one might gain access. In other words, the Fool knowingly betrays Lord Felmet. This foreshadows the moment during the play when the Fool comes forward and bears witness against Lord Felmet for the murder of Verence.