The Powers Of Observation

A professor teaching medicine at the university was tutoring a class on
'Observation'. He took out a jar of yellow-colored liquid. "This," he explained,
"is urine. To be a doctor, you have to be observant to color, smell, sight, and
taste."
After saying this, he dipped his finger into the jar and put it into his
mouth. His class watched on in amazement, most, in disgust. But being the good
students that they were, the jar was passed, and one by one, they dipped one
finger into the jar and then put it into their mouth.
After the last student was done, the lecturer shook his head. "If any of you
had been observant, you would have noticed that I put my 2nd finger into the jar
and my 3rd finger into my mouth."
Lesson learned!