Andy describes coming to the run as the fulfillment of a dream. He has agreed to participate in a study that observes how the body responds in times of acute danger. His heart rate, blood pressure, and cortisol level are measured as part of the assessment. Cortisol is closely related to adrenaline, which may energize Andy to run faster than he ever has before. An hour before the run, he reports he is excited and ready to go. The bulls are released and Andy waits for them to come near. The challenge is to get as close to a charging bull as you dare, without being gored. As the bulls approach, Andy's body is flooded with a massive burst of adrenaline. His cortisol levels more than double. From a resting rate of 72 beats per minute, Andy's heart rate more than triples. Andy describes the fear elicited by the running bulls as incredible. Unquestionably, he has found the experience to be thrilling. The fear instincts that we rely upon to save our lives are very powerful. Thus, concludes the narrator, it is difficult to turn them off at will.