“Cast it before Pharaoh, it will become a serpent” – we learned [regarding] one who stands in prayer: Even if the king greets him, he should not respond to him; and even if a serpent is wrapped around his heel, he should not interrupt [his prayer] (Mishna Berakhot 5:1). What did the Sages see that led them to liken the wrapping of a serpent to the kingdom of Egypt? Rabbi Shimon ben Pazi said: It is as it is written: “Its sound will go like a serpent” (Jeremiah 46:22);4The prophecy in Jeremiah, chap. 46 is stated regarding Egypt. just as a serpent hisses and kills, so too, the Egyptian kingdom hisses and kills, as it places one in prison, falsely accuses him, and kills him.
Alternatively, what did the Holy One blessed be He see that led Him to liken the kingdom of Egypt to a serpent? Just as a serpent is curved [me’ukam], so too, the kingdom of Egypt acts deceitfully. Therefore, the Holy One blessed be He said to Moses: Just as a serpent is curved, so too Pharaoh is deceitful [me’ukam]. When he comes to be deceitful, tell Aaron, and he shall raise the staff before him, as though to say: With this you will be struck.