A small bottle containing urine sat upon the desk of Sir William Osler, the eminent professor of medicine at Oxford University. Sitting before him was a class full of young, wide-eyed medical students, listening to his lecture on the importance of observing details.

To emphasize his point, Sir Osler announced: "This bottle contains a sample for analysis. It's often possible by tasting it to determine the disease from which the patient suffers."

He then dipped a finger into the fluid and brought it into his mouth. He continued speaking: "Now I am going to pass the bottle around. Each of you please do exactly as I did. Perhaps we can learn the importance of this technique and diagnose the case."

The bottle made it's way from row to row, each student gingerly poking his finger in and bravely sampling the contents with a frown.

Dr Osler then retrieved the bottle and startled his students by saying, "Gentlemen, now you will understand what I mean when I speak about details. Had you been observant, you would have seen that I put my INDEX FINGER in the bottle but my MIDDLE FINGER into my mouth!"