This ability of experts to thin-slice accurately depends on years of experience and training. In an earlier Officer.com article, I discussed how experts make complex decisions under time pressure. It turns out that they use two techniques: feature-matching (this looks like something I've seen before) and story-generation (I've never seen this before, so I'll make up an explanation). Scenario-based training can improve both abilities, by giving students a bank of experiences to draw on for feature-matching and by providing a safe environment to try out plausible "stories." Good training can help start novice cops on the way, but only years on the street can truly make them "experts."
However, in one important aspect of experience, even rookie cops have expertise: reading faces. It turns out that facial expressions are universal indicators of emotion, and everybody who isn't autistic knows how to read them. Even if someone adopts a "poker face," attempting to hide what he or she is feeling, facial expressions are not entirely under voluntary control. Truth will emerge, if only fleetingly, as a quick, involuntary, authentic response. But you won't see it if you're not looking. If, for example, you are focused on a suspect's hands, you won't see his face at all.
So am I suggesting that we go back to "Watch his eyes, pardner"? No--I still never heard of anybody being killed by an eyeball. What I am suggesting is that we train officers to use their innate expertise to read faces (and body language) as an early warning system. Too often, we get so focused on procedures, such as how to safely approach a vehicle, or on defensive behaviors, such as watching hands, that we totally ignore the fact that we are dealing with another human being. That person's behaviors, including--maybe especially--facial expressions can give us instant information about potential danger. We can use our expertise as humans to "thin slice" encounters with subjects on the street.
This ability to read faces accurately is innate and unconscious, and like other intuitive senses can be improved with practice--or overridden by conscious choice. Have you ever been faced with a split-second decision, had an initial impulse and then made a reasoned choice against it--only to find out later that your first impulse was right? I sure have. I have a very loud and pushy rational brain, and it's hard for me to shut it up. Reading faces is not an exercise in logic.
Reading people's faces is also not 100% precise. If it were, we'd never be fooled by a smooth-talking salesman. And it's probably not as useful with a sociopath. Someone who does not feel guilt or remorse will not betray guilt or remorse with a facial expression. But for the vast majority of law enforcement encounters, reading the face can be a valuable source of information about what's going on inside someone's mind--before the encounter goes south.
Here's how an officer I worked with described the circumstance of a shooting he'd been involved in. Tim was the backup officer on the call, which was serving a routine warrant on a young man at his parents' home. The primary officer was already on scene when Tim arrived. The parents opened the door and told him, "They're in the basement." Tim said the hair on the back of his neck stood on end, even though nothing untoward had yet happened. He went downstairs and was told that the young man had locked himself in a bathroom. He started back up to see if the parents had a key when the young man burst through the door and fired on the other officer. Tim returned fire, killing the young man and saving his partner's life. Why did Tim's hair stand on end? ESP? Perhaps. But maybe he saw something in the parents' facial expressions that warned him.
So how do we teach our officers to thin-slice effectively? When we put officers through scenarios, often we ask them to articulate the basis for their actions. That's important, because part of an officer's job is to explain the rationale for a response, particularly one involving use of force. What if we instead first asked the officers, "What did you feel?" And when they've answered that question, asked, "What did you do?" Only after they've answered both questions would we ask for a rationale. The goal is to train officers to pay attention to those gut feelings, and act on them, even if (maybe especially if) they can't explain where the feeling came from. If they listen to their "prey" sense, maybe they can take action to control the situation so that it never gets to the point where they have to focus on watching hands.