[The tone makes Cloud narrow his eyes, but then he nods.]

Yeah. It's solidified mako, a form of liquid energy. We've learned how to use it for power in the last few decades... But why mako and materia can make the magical effects if you know how to activate it... [Another shrug. There's lots of theories, of course, and Sephiroth had explained one of them for Tifa's benefit while they were trekking through the caves, but that... Inui will probably just be more confused if he tries to add that. So Cloud chooses not to.]