I’ve gotten a lot of questions about centaur alien respiratory systems now that I’ve animated Talita doing stuff, so here’s a definitive post about them.
The main airway is unidirectional, except for the occasional sneeze. Air enters through the incurrent nostrils on the face, passes into the first air chamber, then to the main lungs that surround the heart and braincase, and then exits out the excurrent nostrils/vents on the rear of the lower ribcage. The majority of oxygen exchange and moisture reclamation happens in the lower lungs, which have a gill-like, high surface area comb structure that the air passes through. Centaurs cool themselves mostly by panting, where they breathe rapidly and open the lung structure up wider in the chest to allow more air to bypass the comb and leave with water and waste heat. They can produce subsonic hums, rattles, and groans out the excurrent nostril by clenching the valve.
The centaur vocal apparatus evolved from an olfactory structure that got co-opted for language. There are still are still scent receptors in it, but the thing has become much more elaborate than in their ancestors. To speak, they breathe into two large sinuses on the back of their head, close those off from the main airway, and compress them to push air out through the trunk. Of the aliens in Runaway to the Stars, centaurs are probably the best at vocalizing human languages. The phonic structure is pretty similar to ours, consisting of vocal cords set in the skull at the base of the trunk, resonant loops back to the incurrent nostrils, and muscular ridges inside the trunk towards the lips. Their large toothed mouth is totally unconnected to the respiratory system, it only leads into the esophagus.