The movement of breath presents a clear picture of how mood may be reflected in the physical body, and vice-versa, how a person’s physical state can influence mood or percep­tion of threat. The sense of stress or physical threat raises our muscle tone, including in the thoracic cavity. Although we are designed to breathe more deeply when we are under short­term threat (the better to run away from danger), long-term, low-grade stress appears to have the opposite effect as the intercostals become locked, and diaphragm moves more shallowly, and the scalenes must do more work to raise the top ribs. This pattern can become ingrained as proprioceptors interpret it as a normal level of tension. Breathing shallowly and with resistance then reinforces any sensation of fear or threat, and the cycle becomes self-fulfilling, even to the point of hyperventilation and involuntary muscle contractions to consume dangerously high levels of oxygen in the blood.