The first thought Sylas had was…
Is the system serious?
He just went through all of this, put his life on the line, was still in the middle of suffering what was probably some warped form of PTSD, all to get this sort of ridiculous choice?
It was clear that the system was obsessed with sparing Professor Fembroise, and it found her to be extremely important, but Sylas simply didn't know whether the system was even trustworthy in this situation.
Even if it rewarded him for sparing her, would it be worth it?
But what almost made him lose control of his temper again was that this very same Quicktime Event could have been given to him the first time. But instead, he had become public enemy number one and was labeled as a traitor by the system.
