Emerald Mine, Day 3

On the night of Day 2, unseen by anyone, a coal seam beneath the Emerald Field begins to smolder. By the time the sun rises on Day 3, the fire is raging underground, visible only at a single fissure near the center of the area—but tributes will hear it long before they see even the plumes of smoke. As hot air is forced through thin fractures in the stone beneath the field, a whistling, ethereal shriek glides over the area, rising and falling like a living scream.

(This specific video was created with metal barrels, but for an example of what this sounds like, see here.)