Is the life of every creature in its blood, including animals, birds, and humans?
Yes. The context states that for everything living under this economy, the life is in the blood. Whether the animal kingdom, the birds, or humans, the blood is the actual source of life that keeps that creature functioning. Genesis 9 ties this to God's instruction to Noah not to eat flesh with its blood.
Les explains from Genesis 9 that after Noah came off the ark, God gave new instructions permitting humanity to kill living things and eat meat, but with stipulations. God said every moving thing that lives would be food, just as the green herb had been given, yet flesh with its life, which is the blood, was not to be eaten. Les emphasizes that under this economy, life is in the blood for the animal kingdom, the birds, and humans: blood is the actual source of life that keeps the creature functioning. The discussion then moves toward I Corinthians 15:50 and Luke 24, where Jesus spoke of flesh and bones.
But flesh with the life thereof, which is the blood thereof, shall ye not eat.