A sword that burns others when they hold it. The idea is intriguing, like something he'd read in the books he shared with Jace, but there were reasons why a blade might do something like that. He just needed to figure out why. Instinctively he knew that some things shouldn't be touched by Mundanes or Downworlders. "Not getting burned by it probably means you're like me genetically."

Which was a nice, 'we're being watched' way of saying they weren't exactly Mundanes. "You could have had it and were planning to give it to someone else or..." He held up one hand, showing Clary the mark like an eye on the back of his hand. "Maybe you didn't take the vow I did or you don't remember being trained in weapons and the sword really is yours."