Watch Carefully Please
1、Harry will never forget his first chemistry teacher in junior high school. 
2、He had strange ways to make his lessons lively and interesting. 
3、Harry still remembers one of the lessons given by the teacher in the chemistry laboratory. 
4、The teacher put out three bottles filled respectively with gas, vinegar and caster oil.
5、Having told the students to watch, he filled a cup with the three liquids. 
6、He stirred and mixed the three together. 
7、Holding up a finger, he asked the students to watch him carefully and then do exactly as he did. 
8、He dipped his finger in the mixture for a few seconds and then put a finger in his mouth. 
9、Sucking the finger, he nodded his head and smiled, looking rather pleased. 
10、He then handed the cup to the students. 
11、Each of them dipped a finger in the mixture and sucked it. 
12、Instead of smiling, they all made faces and spat, for the mixture tasted terrible. 
13、The teacher said to his students sadly, 
'None of you watched carefully enough to see what I did. I did suck a finger, but I did not suck the one I had dipped into the mixture.'”