God instructs Moses and Aaron: take handfuls of soot from the furnace. Moses throws it into the sky before Pharaoh. It becomes fine dust over all the land of Egypt — and from that dust, festering boils break out on every person and every animal.
The magicians who once imitated Moses and Aaron, who declared "the finger of God," cannot now appear before Moses. The boils are on them. They have been removed from the story. Egypt's sacred experts are silenced by the very judgment they acknowledged.
And the text shifts: "the LORD hardened Pharaoh's heart." Until now, the text described Pharaoh hardening his own heart. Now God is named as the agent. The pattern established in the first five plagues has set a course — and God is driving it to its conclusion.