Joel was spending a quiet evening alone reading his favorite book. Suddenly someone burst into the room and shouted his name. His knees became weak, his heart began to pound, and his face flushed red. Joel quickly realized he was happy because the person before him was his brother whom he had not seen in over a year. The next day, Joel encountered another unexpected person. Again his knees became weak, his heart rate increased, and his face flushed. This time he felt afraid, because he was facing a robber holding a gun. These two situations experienced my our hero illustrates the _____ theory of emotion.