Dr. Joseph Bell and The Power of Observation

One of [anatomy professor Dr. Joseph] Bell's favorite tricks [at Edinburgh Medical School circa 1876] was to invite new students to taste an amber liquid in a glass vial. It was, he explained, an extremely potent drug with a vile and bitter taste which they needed to be able to recognize. Since he would not ask students to do anything he would not be willing to do himself, he said that he would be the first. He removed the stopper, immersed a finger into the liquid [his own urine] and then put his hand to his mouth, shuddering as he sucked his finger. The students dutifully followed suit as the vial was passed around, all of them registering disgust. At the end, Bell invariably expressed his disappointment in their poor powers of observation. It was his index finger, he reminded his groaning class, that he had dipped into the noxious brew, but it was his middle finger that he had put into his mouth.

Russell Miller, The Adventures of Arthur Conan Doyle, 2008 [Arthur Conan Doyle attended Dr. Bell's class and used the professor as the model for his fictional protagonist, Sherlock Holmes.]