He didn't have his SCA light on, it was quite possible that Tidus didn't even known he'd been there, but he can't help but come upon a member of the train being snacked on by a rat.

Natsuno grabbed it off of his neck and tossed it aside.

If Tidus looked at him before shining the light on him, he might see that his eyes seemed to glow in the dark slightly, in a way that made him seem more like an animal than a person, but light would dispel that effect. Was it just a trick of the light?

"Be careful."