某教授在田间授课，对同学们说："科学研究要不怕脏......"然后他蹲下来，用手指戳了一下地上的牛粪，然后把手指放到嘴里舔净。众同学都觉得恶心，连连往后退，只有一个同学走上前去说："我不怕脏！"随即也用手指戳了一下地上的牛粪放到嘴里舔净。教授露出了一丝微笑，缓缓地说："另外还要善于观察，我刚才是用中指戳粪，但舔的是食指......"(A professor teaching in the field says to the classmates: "In scientific research, we should not be afraid of to be dirty..." Then he kneels down and pokes cow dung on the ground with his finger, and then lick his finger in his mouth. All the students feel sick, moving back, while only one student steps forward to say: "I am not afraid to be dirty!" Then he pokes cow dung on the ground with his finger, and puts into his mouth to lick. The professor reveals a smile and says slowly: "and, be observant. I just poked dung with middle finger but licked the forefinger..." )