The Myth of Prometheus

One of the astonishing facts about the liver is that the early Greeks knew about this organ’s amazing power to regenerate. We know the Greeks knew because of the myth of Prometheus, which was handed down for thousands of years. Prometheus stole fire from the gods, so Zeus punished Prometheus by tying him up and every day an eagle would peck out his liver. At night, his liver would mend, so the eagle could gnaw at it again the next day. Although this exaggerates the capability of the liver, it illustrates that the Greeks recognized the awesome ability of the liver to recover.

What I want to know is this:

1. What sort of demented torture is this, and doesn’t that suggest that Zeus was really messed up to think this up? Wouldn't water boarding be sufficient?
2. How did Zeus know that the eagle would eat the liver? 
3. Why did the eagle eat just the liver? While he was at it, why not peck at the heart and kidneys? That was one smart eagle if he knew he’d have a continuous source of meat if he just practiced a little self-control.
4. How could the eagle fly away after eating all that liver? The liver weighs 3 lbs, which would have made take-off a bit heavy for the eagle. 

Inquiring minds want to know…