Expiration: Expiration is the quiet expiration normally is a passive process. The inspiratory muscles relax, thoracic cavity volume decreases, and lungs recoil. Since the volume decreases it causes Intrapulmonary pressure to increase. Forced expiration is an active process that uses oblique and transverse abdominal muscles. Nonrepiratoru air movements are processes that can move air into or out of lungs besides breathing. For example coughing, sneezing, crying, laughing, hiccups, and yawns. It has 5 steps. 1st inspiratory muscles relax, 2nd thoracic cavity volume decreases, 3rd elastic lungs recoil, 4th intrapulmonary pressure rises, and lastly air flows out of lungs down its pressure gradient until intrapulmonary pressure is 0.