Zuo Feng's eyes were as wide as saucers. Unlike Yao Xun, who could discern the changes inside the alchemy furnace without even looking, Zuo Feng had to focus all his attention and carefully observe with his eyes to notice any changes within the flames.
This, in itself, was due to Zuo Feng's vision being much stronger than that of ordinary people. If it were an ordinary Martial Artist in the Strong Body Stage, they wouldn't be able to see even the slightest change in the roaring flames. It's as if Yao Xun intentionally wanted to give Zuo Feng the opportunity to observe, hence he didn't cover the top of the furnace.
When Yao Xun infused Spiritual Energy into the furnace to envelop the liquid, he immediately noticed the intense excitement in Zuo Feng's expression. Upon this realization, Yao Xun's expression suddenly relaxed, as if a weight had been lifted off his shoulders.
