Observation!!

1st year students of MBBS were attending their first practical class.They all gathered around the surgery table with a real dead body (man),the professor, put his finger in man's ass and tasted it in his own mouth.

Then he told them to do the same,the students hesitated for several minutes.

But eventually everyone inserted their finger's in man's ass and tasted it,when everyone finished, the professor looked at them and said

Professor: "The most important thing is observation. I inserted my middle finger but tasted the index finger"