Exodus 8:16-19

16 Then the Lord said to Moses, “Say to Aaron, ‘Stretch out your staff and strike the dust of the earth, so that it may become gnats in all the land of Egypt.’” 17 And they did so. Aaron stretched out his hand with his staff and struck the dust of the earth, and there were gnats on man and beast. All the dust of the earth became gnats in all the land of Egypt. 18 The magicians tried by their secret arts to produce gnats, but they could not. So there were gnats on man and beast. 19 Then the magicians said to Pharaoh, “This is the finger of God.” But Pharaoh's heart was hardened, and he would not listen to them, as the Lord had said.

In the first two plagues, the Egyptian sorcerers can imitate the wonders that Moses and Aaron are doing. But here with the third plague and the gnats, Pharaoh’s men are unable to produce them. In fact, Pharaoh’s sorcerers identify what Aaron does as coming from the Lord:

“This is the finger of God” [8:19]

Remember, one of the objectives of the exodus is for the Egyptians and the other nations to learn about the Lord. Here, that objective is beginning to be realized.

And yet Pharaoh still refuses to yield.