Genesis 9:5–6 (ESV)

5 And for your lifeblood I will require a reckoning: from every beast I will require it and from man. From his fellow man I will require a reckoning for the life of man.

Humans are not to eat the blood of animals. The Lord shows in these verses that man is greater than the animals. The blood of a human being may not even be shed. An animal may be put to death, but not a human being. When animals kill a human being, that animal is even called to account and punished in a special way. The Lord will demand the blood of that human being from animals that do so. People are protected from animals.

The next verse shows that, as humans, you are also protected from your fellow humans. We read here an explicit prohibition against killing another. Man has such a special value because God created man in his image. Man is the highest creature. Therefore, the Lord does not want that one man would kill another. Those who do so intentionally must themselves be put to death as punishment.

It is not as if God alone will carry out such a punishment. On the contrary, the Lord makes it clear in Genesis 9:6 that man must shed the blood of that murderer.