Our nervous system assesses threat in two basic ways. First of all, we use our external sense organs to discern and evaluate threat from salient features in the environment. So, for example, a sudden shadow alerts one to a potential risk, while the large looming contours of a bear or the sleek, crouching silhouette of a mountain lion let one know that one is in grave danger. We also assess threat directly from the state of our viscera and our muscles—our internal sense organs. If our muscles are tense, we unconsciously interpret these tensions as foretelling the existence of danger, even when
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