It is said that it is not true that we yawn when we have shortness of breath because we absorb less oxygen when we yawn than when we breathe normally. We simply yawn in our boredom, or really because of our drowsiness. It is also interesting that yawning is contagious, since someone is yawning in our environment, then we will most likely start yawning too. For example, I was already yawning while writing this text. :) According to some research, yawning is also said to increase alertness.