It should be patently clear by now that viviane is looking for tangible stuff. You know, the kind of things scientists can test and measure and stuff.
We know that a body can be revived with shots of adrenalin, electrical jolts to the heart or CPR sometimes. But there is a certain force in the cells of living organisms, that once it is gone, the body/organism cannot be revived. You can put the body on life support machines to keep its blood oxygenated and circulating. You can feed the body nutrients through IV, but if you unhook the life support machines, the body will begin to decompose immediately.
What is it that keeps a body in a still living, revivable state? What is that force? What gives a body life? Why can't we use electricity or adrenalin to revive a body that has lost this force? We know the force exists and that when it's gone, that's it: death, dead, or as Johnny 5 said, "Disassembled!" <....movie reference.
The force in intangible, but we know it exists. Doctors, scientists, us--we all know it exists. What is it though? The only measure or test we have for it is a living, breathing organism and its death. As my mother died, the nurses already had her blood pressure cuff in place so they could determine that she had no blood pressure or heart beat. There are brain wave tests that can be done to see if there is activity left in the brain. The tests, when negative, concur that the death has happened.
There isn't really an instrument to gauge the force that kept the body alive and revivable. Call that force what you will. The force makes animation and life possible and when it is gone, the lack of it makes death complete and irreversible. You can't pour it in a cup and measure the force. You can't see it in blood work. You can't catch it in a balloon. It has no color or smell. You can't catch it with your hand. Still, we know it exists.