Changing the Description!

Ban was visibly startled after seeing that the Beast Core had already shown signs of cracking. 

What does it mean? 

It simply means that Eva had already absorbed a lot of essence for it that it was now beginning to crack. 

It must be noted that not half an hour had passed yet ever since they left the cave. 

The Perfect Harmony State doubled their combat efficiency, training efficiency and cultivating efficiency. 

The combat efficiency was self explanatory while the training efficiency referred to the methods provided by the Book of Techniques for Eva to gain a Skill through specialized training. With the Perfect Harmony State, she will be able to learn Skills twice the normal speed. However, they were still long enough that Ban ultimately decided not to train her using such a method.