God spoke to Moses about the Pharaoh's refusal to free the Israelites. God plans to have Moses unleash the 10 plagues upon Egypt as punishment for the Israelites enslavement and as proof that the Israelites God is real and powerful.
Third Plague: Gnats
Moses and Aaron turn the Nile to blood, killing the fish and forcing the Egyptians to drink elsewhere.
Fourth Plague: Flies
Frogs flood Egypt as Moses foretells, smothering the Egyptians, yet the Pharaoh still refuses.
Fifth Plague: Egyptian Livestock Die
Aaron turns the dust of the land to gnats, yet the Pharaoh continues to be hard of heart.
Egypt was swarmed with flies, ruining the land, as the Pharaoh still continued to keep the Israelites in slavery.
The Pharaoh continued to be hard of heart, and so the Lord caused the death of all Egyptian livestock, but none of Israel died.