An organism that grows in an oxygenated environment. Nestor describes the evolution of aerobic life from its earliest to more advanced forms to emphasize the role of breathing in the development of human life.

Two almond-shaped nodes located in the center of the temporal lobes of the brains of higher-order vertebrates, such as monkeys and humans, the amygdala helps animals make decisions and process emotions. Nestor describes several scientific studies that examine the connection between the amygdala and feelings of fear and panic.

Control system that regulates bodily functions like heart rate, blood pressure, digestion, and respiration, which usually functions automatically or unconsciously. Nestor describes two parts to the autonomic nervous system and its effects on the human body: (1) the parasympathetic nervous system, which stimulates relaxation and restoration using deep, soft, and slow breaths and (2) the sympathetic nervous system, which stimulates action using short, shallow, and hasty breaths.