[ Mitsuru is aware of the presence of another person in the cave with her before she sees him, mainly because whoever it is seems to have a penchant for kicking the strange glowing rocks around. The sound echoes through the cave chamber and she turns her attention to the culprit just as he appears to be examining another of the rocks in his hand.
rocks!
And talking to himself. ]
I would leave them where they are if I were you.