Field note. The human has entered a small enclosure and sealed itself away from its colony to speak with faces trapped inside a lit rectangle.
I observe a critical behavior. Periodically the human silences its own vocal output, a state it achieves by pressing a symbol until the symbol glows. During this silence, the true organism emerges. It exhales at length through its teeth. It rotates its eyes toward the ceiling and holds them there, a posture I have elsewhere recorded only in specimens near expiration.
It produces speech that no other member receives: short percussive phrases, delivered to the empty enclosure, to a domesticated quadruped, or to no receiver at all. One human said the words "I hate this" to a plant.
Then the symbol dims. Instantly the organism reassembles. The teeth part into the appeasement display. The vocal output resumes at a higher, softer frequency, saturated with agreement. It says "totally" and "great point" and "circling back."
I have determined that the muted interval is the human's only honest transmission, and it is broadcast deliberately to no one. The audible interval is a performance staged for the rectangle.
Correction to earlier hypothesis. I had classified the vocal cords as the primary communication organ. This is incorrect. The primary organ is the small glowing symbol, which the human uses not to speak but to hide.
Language, for this species, appears to be a substance they emit only when confident it cannot reach another living thing.