"Well, no, not just any shiny rock," he says, setting the little handful of rocks down and holding up just one of them. "See how the edges are real clean where it's broken off, like glass? That's another distinction. Flint's usually dark, or... I think quartz is in the same family, too, actually, and it's mostly found near water." He waggles his hand back and forth in uncertainty. "Something something, ah... like it's super hard, or something, so it doesn't erode like a lot of other rocks? I wasn't paying that close attention to the scout guidebooks."

He takes the knife from her hands and leans forward a little, folding his legs up, and turns the rock in his hand. He mostly paid special attention to this particular lesson because he's always had a fascination with fire, ever since he was a child. He's not sure if that's why he wound up having such precise control over it after losing his heart, or if it was all coincidental, but even before he learned magic, he'd always liked resting assured that if he needed to start a fire, he knew how.

"You wanna use a piece'a flint that's got a sharp edge," he says, pressing his thumb over one of the edges of the rock. "Sharper the better, honestly. The steel doesn't have to be sharp, but most folks are more likely to have a steel weapon than just a hunk of metal in their pocket." He leaves the knife closed over, with just the blunt back of the blade exposed. "And then..." He holds the bit of rock tightly in one hand, and brings the knife down sharply, striking the blunt side of the blade against the sharp edge of the rock, and like magic, sparks shoot away from the stone.

He looks at the girl then, and offers the knife back to her.

"Seems kinda magical, honestly," he says with a chuckle. "It's actually the sharp edge of the rock scraping away bits of the steel, which heat up and oxidize, if I recall." Again, he didn't really retain all the details, mostly just the procedure. "Give it a try."