Zus had been living in the cold lands for more than a decade. Thus he was possibly the most knowledgeable person there could have been in terms of knowing more about the creatures found there than anyone else.
That being said, Zok was aware of this fact. If he had Zus' knowledge, then he could know exactly what he had to look for to get out of the dungeon. Thankfully, the two of them managed to come to a mutual understanding, as both of them were betrayed by Skah and the shamans.
That pain of betrayal certainly made it easier for them to work together. However, even then Zok's instinctual answer was to kill Zus and take his knowledge for himself. The thought only lasted for a second, but it almost felt as if he had almost given in to the temptation of killing him.
It was a weird feeling almost as if something inside his head wanted to kill Zus. But Zok somehow managed to fight back the urge. He didn't need to kill Zus to think if he was answering his questions honestly or not.
