וַיָּבֹ֨א מֹשֶׁ֤ה וְאַהֲרֹן֙ אֶל־פַּרְעֹ֔ה וַיַּ֣עַשׂוּ כֵ֔ן כַּאֲשֶׁ֖ר צִוָּ֣ה יְהוָ֑ה וַיַּשְׁלֵ֨ךְ אַהֲרֹ֜ן אֶת־מַטֵּ֗הוּ לִפְנֵ֥י פַרְעֹ֛ה וְלִפְנֵ֥י עֲבָדָ֖יו וַיְהִ֥י לְתַנִּֽין׃
모세와 아론이 바로에게 가서 여호와의 명하신 대로 행하여 아론이 바로와 그 신하 앞에 지팡이를 던졌더니 뱀이 된지라
Chibbah Yeteirah
And it became a tanin In the wilderness, which is a place of snakes, the staff was turned into a snake; but in Mitzrayim, which is a place of taninim, it was turned into a tanin. A tanin [תנין] is a "crocodile" in this language, like in Yechezkel 29:3 "The great crocodile [hatanim התנים] that crouches in the midst of his streams". And he didn't do the second sign in front of Par'oh, to bring his hand out from his breast and behold it was afflicted with tzara'at like snow, because if he had been afflicted with tzara'at they would have removed him from Par'oh's presence, and something like this is in Bereishit 50, that Yosef didn't have permission to come before Par'oh when he was still tamei meit before he had buried his father. [In Bereishit 50:4 Yosef lays a petition before the court of Par'oh rather than going directly to Par'oh]
Or HaChaim
ויעשו כן כאשר צוה, They did as G'd had commanded, etc. The reason the Torah writes the words כן כאשר, i.e. repeating basically the same word is, because it tells us that Moses and Aaron a) did what G'd had told them to, b) did not do so until Pharaoh had requested the miracle from them.