[ Oh, he doesn't doubt it's powerful. It's a creepy dragon heart literally still beating despite being removed from the dragon. It's obviously powerful, and John has seen things akin to magic before. John has seen a priestess rise up into pure energy and swipe shuttle crafts clean out of the sky. John has seen enough not to doubt sometimes, people can do impossible things.

Still, he makes a show of thinking about this. ]

I dunno, I mean maybe I'm interested in what you're gonna do with the big dragon. Dragons are pretty cool. Big dragons are even cooler, but I'd think it's hard to keep something that big on a leash.

[ Casual and stupid, that's the way. She's already assumed he doesn't understand anything, so he can feed into that and hope it gets her talking more. He's just awaiting more villain monologuing. ]