And the Lord spake unto Moses and unto Aaron After he had given them their commission, and instructions to go to Pharaoh, and a little before they went in to him:
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"When Pharaoh speaks to you, saying, 'Perform a miracle!' then you shall tell Aaron, 'Take your rod, and cast it down before Pharaoh, that it become a serpent.'"
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Moses and Aaron went in to Pharaoh, and they did so, as Yahweh had commanded: and Aaron cast down his rod before Pharaoh and before his servants, and it became a serpent.