Air movement through a cave is described as breathing when it reverses more frequently than the seasonal reversal of a through-draught in a cave with higher and lower entrances. Slow breathing occurs in response to barometric pressure changes, when the volume of cave air is forced to change. It is notoriously strong in large caves of the Australian Nullarbor Plain. More rapid wind reversals or oscillations, as in Breathing Cave, Virginia, are a resonance phenomenon, similar to the effect produced by air passing over the neck of a bottle. In the cave environment the resonant frequency is relatively low and periodic air flow reversals occur, rather than the sound waves observed at the higher frequencies met in the bottle neck example [9].