Everyone knows that we breathe in oxygen and breathe out carbon dioxide. That's how the respiratory system works. But we also use the respiratory system to produce sound and language. When we speak or emit sound, our glottis opens up, and depending on whether the sound is vocalized, our vocal chords vibrate. We then use articulators (tongue, lips, teeth) to shape the sound we produce.
But what kind of air is emitted in the first place? When our glottis opens up, what kind of air is passing through, and why does it pass through? The most obvious answer, which is my first guess, is that carbon dioxide is passing through our glottis and our trachea, and that we use this to create sound. In this way we would be using the product of respiration for a separate purpose: to create sound and communicate.
This is only a guess. But a logical one. The question, to put it most simply, would be, do we utilize our natural cycle of exhalation to produce sound and speak? Or is something else going on?