Aaron threw down his rod before Pharaoh and it turned into a snake. Pharaoh
summoned the wise men and sorcerers of Egypt... each cast his rod, and they
turned into snakes; and Aaron's rod swallowed up their rods (Exodus 7:10-12)
Why did Aaron's rod swallowed the Egyptians' rods/serpents only after it had
reverted back to its original form, rather than as a serpent itself?
This is to teach us that even when he wages war, the Jew is not a warrior. Even
when he must destroy the serpents of the enemy, he is not a serpent himself,
spewing poison and hate. His instrument of vengeance is as devoid of vengeful
feeling as a lifeless stick.
(From the teachings of the Lubavitcher Rebbe)