Final answer:
The eagle eats Prometheus' liver, which regenerates every night, perpetuating his punishment for giving fire to humanity.
Step-by-step explanation:
In the myth of Prometheus, it is his liver that the eagle is said to eat. Prometheus is a figure from Greek mythology who stole fire from the gods and gave it to humanity. As a punishment, he was chained to a rock, and every day an eagle would come and eat his liver. Since the liver has the ability to regenerate, it would grow back every night, making his punishment eternal.