And if thou refuse to let them go, behold, I will smite all your borders with frogs:

The frogs will be removed from you, from your houses, from your servants and from your people. They will remain only in the river.

Nogef (smite) means destroy. It is thus written, And frogs, which destroyed them (Ps. 78:45). The commentaries are divided as to the meaning of the word tzefarde’im (frogs). Many say that it is a type of fish called al-timsach in Arabic that is found in Egypt, that arises from the river and preys upon people. Others say that it is the well-known sound-producing creature which is found in the majority of rivers. This interpretation appears to me to be correct.

...In connection with the tzfardea it says "only in the river shall they remain."(exodus 8:5) And therefore, (an aquatic creature called) the crocodile remains in it to this day (and it grows there. And they say that sometimes it comes out of the water of the Nile River where it grows. And it comes out on the river's edge and swallows what it finds there - two or three human beings at once. And its body is impervious to spears and arrows unless they are targeted at its stomach. And the doctors said that it is poisonous and touching its body is harmful to a person even if it is dead, and it is a kind of frog and behold, by the power of Moses' words, this creature remains there)...

What are the animals that the scripture called here frogs? Most commentators said that they are the small fish that are constantly making noise in the lakes. And Rabbeinu Chananel explains that they are the great animals of the Nile, called in Arabic "al timsach," but the other commentators of the Torah do not agree with him. In truth, his words seem more fitting than their words. And there are proofs for this from the Torah, for example it says "behold, I will smite all your borders with frogs." (Exodus 7:27) And the term "smite" is only used in connection with the plagues that caused death...

... Furthermore, how could it say "they will remain only in the river,"(Exodus 8:7) which implies that they remained only in the Nile.

But the little screaming fish [frogs] remained in all the other waters of Egypt and also in all the lakes of the world, and all this proves that these tzefarde’im are not the little screaming fish, but the great sea-monster called al timsach, which has the form of a sea-monster...

And today there is an island colonized by the Portuguese Empire, and it is called by the name "island of the crocodiles," because [the crocodiles] emerge from the sea and go out onto the island to hunt for prey to eat. The people of the island fight with them with sword and spear and maces and axes, and [the crocodiles] have eaten most of the children of the people of the island...

...The king of Portugal forced many children of the Spanish exiles to adopt his faith. He sent them to [the island] fourteen years ago; all of them perfectly healthy children, boys and girls, more than two thousand souls. They have already multiplied there, and most of the island is inhabited by them.

... It is known that there are different opinions among the commentaries of the Rishonim with regard to whether the tzefarde’im were the well-known destructive species that is still found today in the river and is called "crocodile", or if it is a species that is found in most of the rivers and shouts and croaks. And according to what I explained above, both interpretations are true. In all the land of Egypt was the second kind and it was not deadly. But in the house of Pharaoh and his people and his servants, the first kind came out of the river and destroyed...

And the crocodile excels in many qualities. It can live a long time in the dry air, so it comes out of the river and dozes on its shore, and often times it runs along the shore for many cubits until it finds its mate in the desert. Likewise, the female lays her eggs on the beach near the river, and when the time comes for the egg to hatch, part of it enters the water and becomes a crocodile, and the part that goes out into the desert becomes an iskinkur

MISHNA: It is written: “Whatever has fins and scales in the waters, in the seas, and in the rivers, you may eat them” (Leviticus 11:9). There is a principle with regard to the signs indicating that fish are kosher: Any fish that has scales has fins; and there are fish that have fins but do not have scales...

It has been clarified by experts in the natural sciences and we can also be seen in nature books that the stinkus is not a sea animal at all, but it grows on land near the sea shore and sometimes it jumps into the sea like a frog and it is a kind of small crocodile, which Rabbeinu Channanel called al timsach, and which, according to his opinion, is the tzfardea that was in Egypt. Therefore, the words of the sages are trustworthy - among fully aquatic creatures everything that has scales has fins.

Moshe and Aharon came to Pharaoh and they did exactly as Hashem commanded. Aharon threw his rod before Pharaoh and before his servants and it became a serpent.

AND MOSES AND AARON WENT IN. This too, namely, that the rod became a tannin (serpent), was a wonder. It was not like the wonder that he did for Israel, as there it only changed into a nachash (serpent).

Pharaoh too called [his] wise men and magicians. The sorcerers of Egypt also did likewise with their magic art.

“Pharaoh also called for the wise men and the sorcerers.” At that moment, Pharaoh began laughing at them and clucking at them like a hen, saying to them: ‘Are these the signs of your God? The way of the world is that people bring merchandise to a place that needs it. Do they bring fish brine to Spain, fish to Akko? Do you not know that all sorcery is in my control?’ Immediately, he sent and brought children from their schools, and they too performed this [wonder]. Moreover, he called his wife and she did so, as it is stated: “Pharaoh also [gam] called.” What is gam? It is that he called even his wife and she did so. “They too [gam], the magicians of Egypt, did so.” What is gam? It is that he called even four- and five-year-old children, and they did so.

Small children were enclothed in the skins of taninim, and they were trained in school in the art of illusion and how to hide under the covering and snatch up the stick, and how to run like a live tanin such that it would deceive one who saw it.

When G-d began creating the word, [G-d] looked into the Torah and created the world.