The existence of gravity.
重力的存在。

1.The reason why flames are going upward is that cold air sinks because of gravity which then results to hot air rising. But if there were no gravity, flames would look like this:
1.火苗向上是因为受重力影响冷空气下沉，热空气上升。但如果没有重力，火苗就是这样：

2.Without gravity bacteria gets tougher. A research shows that salmonella can get 3 times stronger in microgravity. Good thing we have gravity!
2.没有重力的话细菌会更难对付。一项研究显示失重状态下沙门氏菌会强大3倍，真庆幸我们有重力！

3.And lastly, Newton wasn't hit by an apple. He only saw an apple fall to the ground.
3.最后，牛顿并没有被苹果砸中，他只是看见一个苹果掉在地上。

1. One eye blink needs movement of about 200 muscles
1.一个眼睛眨动需要牵动约200个肌肉

2. Every drop of blood in your body is filtered over 300 times in a day
2.身体里每滴血每天都要被过滤超过300次

3. 20 minutes a day outside in a good weather boosts good mood, broadens thinking and improves productivity
3.天气好时一天在户外20分钟能愉悦心情、拓宽思路并提高工作效率

4. Happiness is maximized at 13.9 degrees Celsius
4.快乐会在13.9摄氏度时最大化

5. Surface area of a human lung is equal to a tennis court
5.人一个肺部的表面积相当于一个网球场

6. It is impossible to tickle yourself.
6.胳肢自己是不可能的

7. Olfactory system ( cortex and neurons responsible for interpreting odours) can remember smell of almost 50000 different scents
7.嗅觉系统（负责解读气味的皮层和神经元）能记住约50000种不同气味。

8. Acid in our stomach can dissolve Razor blades
8.我们的胃酸能溶解剃须刀片。

9. Tooth is the only part of the body that can't repair itself.
9.牙齿是身体唯一不能自我修复的部分。