Ex 7:8 Then the LORD spoke to Moses and Aaron, saying,

 9 "When Pharaoh speaks to you, saying, 'Show a miracle for yourselves,' then you shall say to Aaron, 'Take your rod and cast it before Pharaoh, and let it become a serpent.'"

10 So Moses and Aaron went in to Pharaoh, and they did so, just as the LORD commanded. And Aaron cast down his rod before Pharaoh and before his servants, and it became a serpent.

11 But Pharaoh also called the wise men and the sorcerers; so the magicians of Egypt, they also did in like manner with their enchantments.

12 For every man threw down his rod, and they became serpents. But Aaron's rod swallowed up their rods.

13 And Pharaoh's heart grew hard, and he did not heed them, as the LORD had said.


God permitted the wise men, sorcerers, and magicians through Satanic power to turn their rods into serpents to harden his heart.

Now, this is a creative act right here. Question: "Does Satan have creative powers?" No, only God has the power to create. Personally, it appears that God granted Satan with some creative powers to harden Pharaoh at this point.   

Seeing that the miracle was something that his own magicians could replicate, even though their rods were swallowed up, Pharaoh's heart grew hard.