Desire

While Lin Mu was focused on his mind, the pair of mother and son were seeing something completely different. At first, they thought that Lin Mu was simply gonna demonstrate his skill of using a spirit sword with his spirit sense. 

But they had completely misunderstood it.

Lin Mu was trying to emulate what he had seen Old man Jing Wei do when he went to buy the short sword and knew that he could do it after seeing the progress he had with the thousand armament blade Scripture.

He had known that the Thousand armament blade scripture was what both Jing Wei and Duan Ke's techniques were derived from and were inferior versions of. He guessed that he wouldn't be at the level of Jing Wei of course, but if he could demonstrate even one percent of that, Lin Mu would be happy.