"It gets hard to sort out the genuinely quasi-magical from mere wishful thinking," says Bridget, returning with a large, sharp knife. "But I've seen a thing or two. Nothing as immediately visually impressive as this, however."

She presses the edge against her arm with obvious force. It makes a polite sort of dent, the kind you might get from poking yourself with your finger. And in much the same way, a paler line along her skin is briefly visible when she drags it away.