Midrash su Isaia 27:1

And Aaron forthwith cast down his rod before Pharaoh and before his servants, and it became a serpent (Exod. 7:10). Whereupon Pharaoh said: “Is this the full power of your God? Why, my magicians travel throughout the world performing such feats.” Then Pharaoh called also (ibid., v. 11) the youths, and babes of five, yea, even of four years, and each of them cast his rod. It is written: Pharaoh called also because he disdained at first to summon his magicians and sorcerers. Our sages of blessed memory said: He actually performed a great miracle with that rod. When one serpent is able to swallow other serpents, that is not unusual, but this serpent turned itself back into a rod again, as it is written: But Aaron’s rod swallowed up their rods (ibid., v. 12). If a man made bundles out of the rods that were cast to the ground to become serpents, there would have been more than ten bundles, yet Aaron’s rod swallowed them all and it became no larger than it was previously. When Pharaoh beheld that, he was amazed and exclaimed: “Surely if he should command the rod to swallow Pharaoh and his throne, it could swallow them.” That was the sign that He had given to Moses at the bush when He said: This which is in thy hand, cast it to the earth (ibid. 4:2). The word this alludes to Pharaoh, who is compared to a snake, as is said: The Lord with His sore and great and strong sword will punish leviathan the slant serpent (Isa. 27:1). When Moses withdrew from Pharaoh’s presence, the wicked one said: “If this son of Amram comes near me again, I will slay him, I will hang him, I will burn him.” That is why, when Moses returned, Pharaoh became like a rod. And Pharaoh’s heart was hardened, and he harkened not unto them, as the Lord had spoken (Exod. 7:13). With reference to the first five plagues, the words Pharaoh’s heart was hardened, etc., are written, but after the fifth plague occurred and he still would not permit them to leave, the Holy One, blessed be He, said: Henceforth, even if he desires to send them away, I will not allow it. Hence, with reference to the last five plagues it is written: But the Lord hardened Pharaoh’s heart (ibid. 10:20). Moses decreed what was to transpire, and the Holy One, blessed be He, executed it, as it is said:: Thou shalt also decree a thing, and it shall be established unto thee (Job 22:28).

...A royal lady once approached Rebbi Yosi. She said, “My god is great than yours!” He retorted, “And why?” When your God appeared to Moshe at the burning bush, Moshe had to cover his face,” She explains. “But when he first saw my god, the snake, he immediately ran away”. Rebbi Yosi replied, “May your bones disintegrate! When God revealed himself by the burning bush, he had nowhere to go—where would he run off to? The heavens? Sea? Dry land? Does God not fill the heavens and the earth! (Yermiah 23:24). A snake—a snake which is your god, as soon as one takes three or four steps away, he is saved!”

(Gen. 1, 21) And God created the great sea monsters. Here in Babylon they translate this "sea gazelles." R. Jochanan, however, said: "It means leviathan— leviathan male and female, as it is written (Is. 27, 1) On that day will the Lord punish with His heavy and great and strong sword leviathan the flying serpent, and leviathan the crooked serpent, and He will slay the crocodile that is in the sea."

R. Juda, in the name of Rab, said: "All that the Holy One, praised be He, created, was male and female, and also the leviathan — the flying serpent male, and the crooked serpent female; and if they should have intercourse they would destroy the world. What did His Holy One, praised be He! do [to prevent this]? He made the male impotent, and killed the female and salted it for the righteous in the future world, as it is said (Ib.) And He will slay the crocodile, etc. And also (Ps. 50, 10) the cattle upon a thousand mountains. He created them male and female, and if they should have intercourse, they would destroy the world. Therefore, the Holy One, praised be He! rendered the male impotent and rendered cool the female, and preserved it for the righteous in the future world, as it is said (Job 40, 16) Only see [how great] is the strength in his loins, referring to the male, and his force in the muscles of his belly, referring to the female. But why did He not render cold the female of the leviathan also? Because a salted female has a better taste. And why did He not salt the females of the cattle in question? Salted fish gives a good taste, but salted meat does not.

On the fifth day He brought forth from the water the Leviathan, the flying serpent, and its dwelling is in the lowest waters; and between its fins rests the middle bar of the earth. All the great sea monsters in the sea are the food for the Leviathan. Every day it opens its mouth, and the great sea monster destined to be eaten that day (tries) to escape and flee, but it enters the mouth of the Leviathan; and the Holy One, blessed be He, plays with it, as it is said, "This is the Leviathan, whom thou hast created to play with him" (Ps. 104:26).