Holmes:“I followed you.”
Suspect: “I saw no one.”
Holmes:“That is what you may expect to see when I follow you.”—“The Adventure of the Devil’s Foot”
In the science of physics, it’s a well-known phenomenon that the act of observing may itself change that which is being observed. The same phenomenon is demonstrable in detective work: It is always preferable that the detective observe unobserved, lest a suspect redouble his efforts to remain hidden and the task at hand be compromised. When appropriate, therefore, consider applying the following obfuscational techniques.
* Disguise your identity. With luck, a convincing and frequently changing disguise will prevent suspects from realizing they are being shadowed. Disguises are especially vital for celebrated detectives whose features may be well known to the public; ever since Watson began writing about Holmes’s cases, Holmes complains in The Sign of the Four, he “can only go on the war-path under some simple disguise” for fear of being recognized.
* Sneak, skulk, and steal. Make liberal use of rear entrances and garden walls, over which a fit detective should be able to scramble. Develop your knowledge of metropolitan alleyways, side streets, and tunnel systems—“It is a hobby of mine to have an exact knowledge of London,” Holmes boasts in “The Red-Headed League”—and travel by them in favor of major thoroughfares, whenever possible.
* Silence your shoes. The acoustic propagation of your footfalls may be dampened by gluing felt or soft rubber to the soles of your shoes. Or simply wear shoes that are naturally dampened, as Holmes advises Watson to do when sneaking into the home of a notorious blackmailer in “Charles Augustus Milverton.” “I have a pair of rubber-soled tennis shoes,” Watson says. “Excellent,” replies Holmes.
