"Shh." The sound is immediate; the voice it comes from is high, young. Her next words come in a half-whisper. "They can't see, but they can hear just fine."

There's a rumbling beneath them both. The earth vibrates -- though not from an earthquake. It's too localized for that. Something is coming, pressing its way through the rock.

The sound vibrates up through the walls, thudding through the enclosed space.