Verses 16-19 “16And the LORD said unto Moses, Say unto Aaron, Stretch out thy rod, and smite the dust of the land, that it may become lice throughout all the land of Egypt.
17And they did so; for Aaron stretched out his hand with his rod, and smote the dust of the earth, and it became lice in man, and in beast; all the dust of the land became lice throughout all the land of Egypt.
18And the magicians did so with their enchantments to bring forth lice, but they could not: so there were lice upon man, and upon beast.
19Then the magicians said unto Pharaoh, This is the finger of God: and Pharaoh’s heart was hardened, and he hearkened not unto them; as the LORD had said.”
17And they did so; for Aaron stretched out his hand with his rod, and smote the dust of the earth, and it became lice in man, and in beast; all the dust of the land became lice throughout all the land of Egypt.
18And the magicians did so with their enchantments to bring forth lice, but they could not: so there were lice upon man, and upon beast.
19Then the magicians said unto Pharaoh, This is the finger of God: and Pharaoh’s heart was hardened, and he hearkened not unto them; as the LORD had said.”
The third plague (lice), which came from the dust, was a miracle which the magicians of Pharaoh could not copy. They could make people think that they were producing blood and frogs, but they could not trick people about the production of lice. There is a limit to both Satan’s power and the ability of corrupters of the things of God to “trick” people through slight of hand.