Scenarios 1 & 2 described in the OP are reasonably straightforward:
- Blood must be removed before meat is eaten. This is true.
For example, Leviticus 17: 13
And whatsoever man there be of the children of Israel, or of the strangers that sojourn among you, which hunteth and catcheth any beast or fowl that may be eaten; he shall even pour out the blood thereof, and cover it with dust.
See additional passages in the excellent appendix provided by Dottard.
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- Can blood no longer in the flesh be consumed? -- this was not permitted
The preceding verse in Leviticus leaves litter room for doubt:
12 Therefore I said unto the children of Israel, No soul of you shall eat blood, neither shall any stranger that sojourneth among you eat blood.
Whether or not it was still in the flesh was not relevant; consumption of blood was prohibited.
The third scenario is less obvious, hence the development of rabbinic exposition on the matter, as discussed by Nhi. Later rabbinic tradition declared explicitly what was implicit in the command in Genesis 9/Leviticus 17: don't eat the flesh of an animal that is still living.
But how would this conclusion have been reached?
I suggest the key word in Genesis 9:4, and indeed in the aforementioned passage in Leviticus, is "nephesh" (נֶפֶשׁ) or "life". The Torah indicates repeatedly that the life is in the blood of the creature. Nephesh is a word that, like its Greek counterpart ψυχή ("psuché"), carries several meanings.
Nephesh is sometimes used to refer to a living being, self, emotion, or to life itself, and, interestingly, even to the breath of life or the being that breathes (see discussion by BDB here).
The emphasis here is that one should not consume a living being. Ellicott's commentary is insightful:
The words are remarkable. “Only flesh in its soul, its blood, ye shall
not eat.” The Authorised Version is probably right in taking blood as
in apposition to soul, which word means here the principle of
animation, or that which causes an animal to live. This is God’s
especial gift; for He alone can bestow upon that aggregation of solids
and fluids which we call a body the secret principle of life. Of this
hidden life the blood is the representative, and while man is
permitted to have the body for his food, as being the mere vessel
which contains this life, the gift itself must go back to God, and the
blood as its symbol be treated with reverence.
The body is for man to eat; the nephesh is not.
This is implicit in the words used in the Torah; it was made explicit in later rabbinical teaching--option 3 is prohibited; one should not consume the flesh of a living animal.
- The practical effect is merciful: draining the blood is a foolproof way to make sure the animal is dead before it is dismembered
- The symbolic effect is instructive: life is a gift from God, to be treated with reverence. Indeed, the passage in Leviticus teaches:
it is the blood that maketh an atonement for the soul (Lev. 17:11)
This finds Old Testament application in the Levitical sacrifices and New Testament application in the atoning blood of Christ.
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Conclusion
The reverence for life taught in the Torah explicitly bans the consumption of blood, and implicitly bans consuming anything until its life has been removed/extinguished. This would therefore rule out swallowing an animal whole, removing & consuming a limb from a living animal, or biting into a corpse without proper preparation. The command is hygienic to humans, merciful to animals, and symbolically instructive: life is a gift from God and is to be respected.
The scenario posed of skinning fish alive is not directly addressed in Genesis 9:4, but I struggle to see how one who understands and adheres to the symbolism above could do it. It may not be spelled out in the letter of the law, but it certainly runs contrary to the spirit of the law.
Appendix--a point of scientific interest
The Biblical concept of "breath" or "spirit" (same word in Hebrew, also same word in Greek) is the entity that gives life--it is combined with inanimate clay to make a living being.
In modern times we are aware that the substance in the air that permits animal life is oxygen, and it is carried by the blood to provide life-giving sustenance to the cells throughout the body. The blood literally does carry the breath of life.
Whether this means the breath of life is in the blood (oxygen carried by the blood), or it means that the blood is the thing that allows the breath of life to interact with the flesh, the Biblical parallel is striking.