Yawning is considered a non-respiratory gas movement. A non-respiratory gas movement is another process that moves air in and out of the lungs that don't include breathing. Yawning is a reflex that tends to disrupt the normal breathing rhythm and is believed to be contagious as well. The reason why we yawn is unknown, but some think we yawn as a way to regulate the body’s levels of O2 and CO2. Studies done in a controlled environment with different levels of O2 and CO2 have disproved that hypothesis. Although there isn’t a concrete explanation as to why we yawn, others think people exhale as a cooling mechanism for our brains. Studies on animals have supported this idea and it is possible humans could be linked to it as well. What is known is that yawning does ventilate all the alveoli in the lungs.