Feeling is a very difficult sense to tune up, particularly when living and working in crowded environments. This is why pickpocket teams are so successful. One bumps ("stalls") you, and a second takes your wallet ("dips") and passes it off to a third (and perhaps even a fourth) person. A simple self-test to determine if your "feel" indicator is up and alert is to try discerning the wind direction at any given time.

One last sense that strongly goes with defensive tactics is your ability to smell. People have odors, and if you haven't seen them or felt them through contact or air currents, you can often smell them. For example, fear has a smell. In searching houses for fugitives, I often could smell their fear, which, for me, has the smell (and taste) of brass. Along with this smell of fear often comes stomach and intestinal tract disruption, so you get burps, stomachs growling and methane gas.

Also, the various colognes, perfumes and deodorants worn are quite noticeable, particularly when the wearers are using them to cover up a lack of personal hygiene. Smokers leave odor trails and wear the odor of burned tobacco.

At this point, it is reasonable to ask, "Who wants to live like this?" Well, the predators do, and wishing you didn't live in the same world will not make it so. The solution is learning these defensive tactics and practicing them till they become habitual.

Of course, these tactics do have to replace existing habits, many of which run counter to good defensive tactics (like walking around tuned in to various wireless devices, as I cautioned against earlier).

The learning curve isn't all that steep, though, and as you redevelop these sensors, you can then expand your ability to gather information under more difficult conditions, such as in darkness and in crowds like those found in airports and shopping malls. In such places, you are forced to make micro-second evaluations, discarding the unimportant lest you lock up due to information overload.

I'll leave you with this thought, a truism uttered in the 1998 movie "Ronin" by its protagonist, Robert De Niro, playing a former CIA field officer: "Whenever there is any doubt, there is no doubt."