Why?!

Su Ming used the tribe leader as a guide to help him locate the reinforcements from Black Mountain Tribe, then right before their eyes, he cruelly killed their tribe leader and beheaded him. He made sure to exaggerate his movements, and with that strange look of his under the full moon, his advantage over Black Mountain Tribe reached its peak in an instant.

Su Ming had to do it. He was already incredibly tired. Even if he had the nourishment provided by the moon, he still had to spare strength to kill Shan Hen. He hated that traitor who had escaped into the forest after being injured.

Thus, he had to take into account how to complete his mission with his remaining stamina and why he decided to use psychological warfare.