Air movement in caves is a common occurrence. Cool air displaces warm air seasonally, for example, and barometric pressure shifts cause cave air to stir. A breathing cave features a particular kind of air movement, a resonance phenomenon most easily understood by blowing across the opening of a bottle. Inside the bottle, successive waves of high and low air pressure vibrate with such rapid frequency that they produce an audible sound wave. A breathing cave, with its analogous shape, exhibits the same phenomenon on a larger scale. Air moving across the cave opening triggers an undulating movement of air inside, but the cave’s greater volume slows these undulations so dramatically that what is created is not a sound wave but a rhythmic periodic “breathing.” Cavers can feel this breath on their hands and face or might watch it sway a candle ﬂame. This is how Virginia’s Breathing Cave got its name.