Blood?

Similar to the previous parts this area was pitch dark and Lin Mu was using his spirit sense to 'see'. But unlike the others, this area was so large that his spirit sense was only able to feel the air and the ends were not visible to him.

"This area is at least a hundred meters wide." Lin Mu muttered. 

He extended his spirit sense upwards and finally felt the roof of the cave. But even then it was quite far up as Lin Mu had walked a large distance downwards. He wanted to continue but felt hesitant as his spirit sense did not seem to be able to perceive everything.

There could be things that were beyond his spirit sense that may be dangerous to him. Not wanting to continue directly he took out a torch from the ring. He gestured with his hand and suddenly heard a shout in his mind.

"NO! Stop!" Xukong yelled, but was too late.

A spark appeared in Lin Mu's hand and then "BOOOOOM!"