Holmes, however, has an idea. “Of course, this blood belongs to a second individual—presumably the murderer, if murder has been committed,” he tells the two policemen. “It reminds me of the circumstances attendant on the death of Van Jansen, in Utrecht, in the year ’34. Do you remember the case, Gregson?” Gregson confesses that he does not. “Read

This is the scientific method at its most basic. Holmes goes a step further. He applies the same principle to human beings: a Holmesian disciple will, “on meeting a fellow-mortal, learn at a glance to distinguish the history of the man and the trade or profession to which he belongs. Puerile as such an exercise may seem, it sharpens the faculties

Indeed, priming studies can be notoriously difficult to replicate: bring any attention at all to the priming mechanism, and you’ll likely find the effect go down to zero. When we are aware of the reason for our action, it stops influencing us: we now have something else to which to attribute whatever emotions or thoughts may have been activated,

Those steps are called retrieval and reconsolidation, respectively.

Who has touched what, what has come from where, what is there that shouldn’t be, and what isn’t there that should be. He remains capable of extreme objectivity even in the face of extreme circumstances. He remembers his goal, but he uses it to filter and not to inform. Watson, on the other hand, is not so careful.

“It is surprising that people do not believe that there is imagination in science,” he once told an audience. Not only is that view patently false, but “it is a very interesting kind of imagination, unlike that of the artist. The great difficulty is in trying to imagine something that you have never seen, that is consistent in every detail with

(1) thinking ahead, or viewing the situation as just one moment on a larger, longer timeline and being able to identify it as just one point to get past in order to reach a better future point; (2) being specific and setting specific goals, or defining your end point as discretely as possible and pooling your attentional resources as specifically

All that detail, but nothing that makes a difference to the task at hand—his choice of future flatmate.

Holmes’s trick is to treat every thought, every experience, and every perception the way he would a pink elephant. In other words, begin with a healthy dose of skepticism instead of the credulity that is your mind’s natural state of being.