Damian kept looking at them, trying to figure out what they were whispering about. At some point, he realized something. He saw that the girl looked at him for a brief moment, right into his eyes.
"Can she see me?" he thought.
That was the only explanation for her behavior. Damian, after realizing this, took a closer look at everything she had done.
He started walking too, not staying in the same place. That way, she would have to whisper back to Mathias if he did something weird. Mathias couldn't see in the dark after all.
Damian decided to take out the ritual dagger and show it to them. He had it in his hands, as if he was about to go and attack them with it.
The girl had stopped whispering to Mathias, but when she saw that, she whispered again.
"Yeah, she's definitely seeing me," Damian thought.