十万个为什么·科学启蒙30篇（3）
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Your Nose Sends an Emergency Signal
鼻子发出紧急信号，你就打喷嚏
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When dust, pollen, or cold air tickles your nasal passages, nerves send a fast alert.
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Your brain tells your lungs to take a deep breath and push air out hard.
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Muscles in your chest, throat, and face all squeeze together in one quick motion.
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That rush of air shoots out at over 100 miles per hour to clear irritants.
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Your eyes close automatically during the sneeze to protect them from germs.
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Covering your mouth with your elbow helps stop tiny droplets from flying far.
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Some people sneeze when they walk into bright sunlight — scientists call this the photic reflex.
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Sneezing too often might mean allergies or a cold is starting.
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It’s polite to say 'Excuse me' right after you sneeze in public places.
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Doctors suggest washing hands often because sneezes spread germs easily.