Exodus 8

It looks as if God is peeling back the layers of falsehood covering this interaction. With the frogs, Pharaoh concedes to let the Israelites go if the frogs will just go away (although, he goes back on his promise). With the gnats, the Egyptian magicians are unable to duplicate the miracle. With the flies, Pharaoh offers to let the Israelites sacrifice to God within the land of Egypt (though this is not enough). God is chipping away at Pharaoh's heart of stone.