...Here and there little groups formed, and sometimes they clicked together in still other monstrous geometric shapes, yet always they moved with an uncanny stillness, darting with utter sureness among the scattered rocks...

The tetrahedra meanwhile glided about their endless affairs, forming and reforming in geometric pattern. Or they clicked swiftly into many-faceted forms that in turn mounted into monolithic, crystalline monstrosities, then melted with startling suddenness into their original components. These were idle, pointless maneuverings from the human viewpoint, yet fraught with some hidden meaning and purpose as alien to Earth as the things themselves...

('Tetrahedra of Space' by P. Schuyler Miller)

Then came their speech-of all things the most mindwracking! I felt it deep within my brain, before I sensed it externally, a dull, heavy rhythm of insistent throbbing, beating at my temples and throwing up a dull red haze before my staring eyes! And then I knew it was no fancy-that the great things of the blasted valley were indeed speaking, chanting, in low, vibrant monotone that beat physically upon me in long, slow waves of the air! You have heard those deepest notes of a great organ, when the windows tremble, even the walls, the building itself vibrate in resonance, beat and beat and beat to its rhythm until you feel it throbbing against your skull, pulsing in your mind in a vast, relentless sea of thundrous sound!