 Not only does such joking foster rationality and provide pleasure, but it reduces or eliminates the combination of fear and/or anger called “stress,” which is at epidemic levels in the industrialized world. In fear and anger, chemicals such as epinephrine, norepinephrine, and cortisol are released into the blood, causing an increase in muscle tension, heart rate, and blood pressure, and a suppression of the immune system. Those physiological changes evolved in earlier mammals as a way to energize them to fight or flee, and in early humans, they were usually responses to physical dangers such as predators or enemies. Today, however, our bodies and brains react in the same way to problems that are not physically threatening, such as overbearing bosses and work deadlines. The increased muscle tension, the spike in blood pressure, and other changes in stress not only do not help us with such problems, but cause new ones such as headaches, heart attacks, and cancer. When in potentially stressful situations we shift to the play mode of humor, our heart rate, blood pressure, and muscle tension decrease, as do levels of epinephrine, norepinephrine, and cortisol. Laughter also increases pain tolerance and boosts the activity of the immune system, which stress suppresses (Morreall 1997, ch. 4; Morreall 2016, ch. 5–6). 