Sometimes, the fundamental tone would rise and fall, as if the mountain were playing a tune for them. Volcanic vibrations resonated in this chamber and, as the magma pool rose and fell, so did the fundamental tone. There is no physical reason why such a subterranean trombone cannot play in the audible range. Such a mechanism might explain some of the mysterious hums heard in various localities, such as the Taos hum. Ordering information here .
Some animals can hear infrasound.
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