Before launching into the ten plagues, Moshe and Aaron demonstrated to Pharaoh that God was on their side by transforming a staff into a snake, and then back into a staff. But why would a magic-show trick prove that God was on their side?
The Noam Elimelech points to an anomaly in the verse (Ex. 7:9) offering us a clue as to why Pharaoh might have taken them seriously. Of course, sleight-of-hand was never going to impress Pharaoh, the king of the tricksters — but the test Pharaoh set for them was at a much higher level, as Rabbi Dunner explains.