It had been a rhetorical question, really; Dean has his own problems, none of which he can really solve, so he's been pretty lax about taking on anyone else's problems. But something Titus said catches his attention, stilling the small settling motions he was making to try to find a way to sit that causes the least amount of throbbing.

"Demon, huh?" Dean does not, exactly, sit up and pay attention; demons are certainly directly pertinent to his interests, but Titus is clearly not a hunter, and civilians tend to call all sorts of things demonic. Could be simple as a hallucination, but old, ingrained instincts won't let the possibility of real demonic interference with an innocent pass by unchallenged, so Dean cocks his head to one side and tries to look less bitchy. "How'd you come to that conclusion?"

He doesn't sound skeptical. Just curious.