A merchant in a small town had identical twin sons. The boys worked for their father in the store he owned and when he died, they took over the store. Everything went well until the day a twenty-dollar bill disappeared. One of the brothers had left the bill on the counter and walked outside with a friend. When he returned, the money was gone. He asked his older brother, "Did you see that twenty-dollar bill on the counter?" His older brother replied that he had not. But the young man kept questioning him. "Twenty-dollar bills just don't get up and walk away! Surely you must have seen it!". There was subtle accusation in his voice. Anger began to rise. Hatred set in. Before long, bitterness divided the twins. They refused to speak. They finally decided they could no longer work together and a dividing wall was built down the center of the store. For twenty years the hostility grew, spreading to their families and the community. Then one day a man from another state stopped by the store. He walked in and asked the younger brother, "How long have you been here?" He replied that he'd been there all his life. The customer said, "Twenty years ago I came into this town in a boxcar. I hadn't eaten for three days. I came into this store and saw a twenty-dollar bill on the counter. I put it in my pocket and walked out. All these years I haven't been able to forgive myself. So I had to come back to return it." The customer was amazed to see tears well up in the eyes of the man. "Would you please go next door and tell that same story to the man in the store?" the younger brother said. Then the customer was even more amazed to see the two middle-aged men hugging each other and weeping together in the front of the store. After twenty years, the brokenness was repaired. The wall of anger that divided them came down.

Chewing leads to smaller particles for swallowing, and more exposed surface area for digestive enzymes to act on. In other words, it means the extraction of more fuel and raw materials from a mouthful of food. This is especially important for mammals because they heat their bodies from within. Chewing gives mammals the energy needed to be active not only during the day but also the cool night, and to live in colder climates or places with changing temperatures. It allows them to sustain higher levels of activity and travel speeds to cover larger distances, avoid predators, capture prey, and make and care for their young. Mammals are able to live in an incredible variety of habitats, from Arctic tundra to Antarctic pack ice, deep open waters to high-altitude mountaintops, and rainforests to deserts, in no small measure because of their teeth.