The sense of sound is one of our most important means of knowing what is going on around us. Sound has a waste product, too, in the form. of noise. Noise has been called unwanted sound. Noise is growing and it may get much worse before it gets any better. Scientists, for several years, have been studying how noise affects people and animals. They are surprised by what they have learned. Peace and quiet are becoming harder to find. Noise pollution is a threat that should be looked at carefully. There is a saying that it is so noisy that you can't hear yourself think . Doctors who study noise believe that we must sometimes hear ourselves think. If we don't, we may have headaches, other aches and pains, or even worse mental problems. Noise adds more tension(紧张)to a society that already faces enough stress. But noise is not a new problem, In ancient Rome, people complained so much about noise that government stopped chariots(四轮马车) from moving through the streets at night! Ways of making less noise are now being tested. There are even laws controlling noise. We cannot return to the 'good old days' of peace and quiet. But we can reduce noise- if we shout loudly enough about it. Why are scientists surprised by the findings in their noise study? ______