Comments on Book 11-12 ( My original post might had a editing issue )

At the end of Book 11, there was a reference to Cheiron which according to my research is an important Godly figure that Achilles has had the honor of training under him for being the warrior that he is now. Book 11 describes the details of this ongoing battle and confusion along with the interference of Zeus, and I wasn't sure why Zeus started this panic by making it rain blood on all the people. Maybe Zeus was testing the power of each of the fighters to see who was the bravest? Or maybe to give a second chance to Hektor?
The Acheans had anger towards Zeus and Hektor since they were losing the battle and were not as strong as they thought, aiming to get rid of Hektor even though that wouldn't have made the Trojans weaker since they had the most prepared men for battling.