Midrash su Deuteronomio 14:9

6) (Vayikra 11:9): "This you may eat": to include a clean fish (found) in the maw of an unclean fish. I might think that also (included as permitted) is an unclean fish in the maw of a clean fish; it is, therefore, written (Vayikra 11:9) "those (clean fishes themselves) (you may eat"), (and not unclean fishes swallowed by them). Why do you see fit to say vis-à-vis beasts (see Chapter 3:3 and Vayikra 11:4) that (a clean beast) in the maw of an unclean beast is unclean, and that (an unclean beast) in the maw of a clean beast is clean, whereas vis-à-vis fish, (an unclean fish) in the maw of the clean fish is unclean, and (a clean fish) in the maw of an unclean fish is clean? — Because it (what is found inside the fish) did not grow there, (but was just swallowed, as opposed to the instance of the beast). "you may eat": to include a clean fish which was pickled together with an unclean one. I might think that this were so even if it (the unclean fish) dissolved (into the brine); it is, therefore, written (Vayikra 11:4) "those [clean fish by themselves] (you may eat"), (and not the forbidden element that they have absorbed).

(Exod. 34:27:) <AND THE LORD SAID UNTO MOSES:> WRITE DOWN THESE WORDS, [FOR ORALLY IN THESE WORDS…. ]⁸⁵On the translation of this verse, see above, note 76. R. Johanan, R. Joshua, and R. Simeon say: "{I gave you} [With] <these> words" is not written here, but ORALLY IN <THESE> WORDS. I gave you Written Torah and Oral Torah. If you make what is in writing oral and what is oral into writing so as to reverse them, you will not receive a reward. Why? Because I gave you Written Torah and Oral Torah. I also made a covenant with you with the stipulation that you recite them in this way; but if you change it, know that you will invalidate the covenant. Thus it is stated (in Deut. 4:9): LEST YOU FORGET THE THINGS THAT YOUR EYES HAVE SEEN, <things> which are written down in writing. (Ibid. cont.:) AND LEST THEY DEPART FROM YOUR HEART. These are < words > that are oral.

(Devarim 14:9) "This may you eat … (12) and this you may not eat, etc.": R. Akiva said: Was Moses a hunter or an archer (that he knew the signs of all the animals in creation)! Let this serve as a riposte to those who say there is no Torah from Heaven!