If psychopaths were easy to spot, there wouldn't be so many of them working successfully in business. Recent research reveals that something like one in five CEOs is a genuine psychopath. Obviously, a lot of the extremely empathy-challenged manage to pass as normal people.

So if you can't count on psychopaths being obvious, axe-wielding predators, how do you identify them? First, know when to keep your guard up by familiarizing yourself with the research on just how common the condition is in certain professions. Then learn the list of traits psychologists use to identify psychopaths.

However, even these checklists can sometimes fail you. Psychopaths are often super charming, seasoned manipulators, who learn to hide the lack of empathy and remorse that makes them so dangerous pretty quickly. But according to science, there are a few signs beyond the basics that few of us--including, you'd imagine, few psychopaths--are aware of.

So what are these subtle giveaways that your local psychopath probably doesn't know they need to cover up? PsyBlog recently included three in a longer list of scientifically validated signs.

1. Late nights

Obviously, not every night owl is a psychopath, but psychopaths are more likely to stay up late, according to science. So if you're already suspicious of someone in particular, knowing they're up until all hours could be another bit of evidence that you might just be right.

PsyBlog quotes Peter K. Jonason, one of the researchers who documented the correlation, to explain the phenomenon: "Those who scored highly on the Dark Triad traits [narcissism, Machiavellianism, and psychopathy] are, like many other predators such as lions and scorpions, creatures of the night. For people pursuing a fast life strategy like that embodied by the Dark Triad traits, it's better to occupy and exploit a low light environment where others are sleeping and have diminished cognitive functioning."

2. Coffee addiction

Again, a great many coffee addicts are not psychopaths (I hope not, at least, as I'm married to one), but science has found a link between enjoying strong, bitter tastes and psychopathy.

"Having a preference for bitter tastes is linked to psychopathy, narcissism, and everyday sadism, a new study finds," reports PsyBlog. "A predilection for tonic water or coffee, therefore, could indicate some psychopathic tendencies in a person's personality."

In contrast, people who dislike bitter tastes tend to be more agreeable, the researchers discovered.

3. No sympathy yawns

We all know psychopaths lack empathy, but few realize that this trait shows up even in small, everyday actions that are predicated on noticing and caring for others--actions such as yawning after someone else does, for example. What's natural for normal folk is apparently less common among psychopaths. PsyBlog points to a "study [which] found that people with psychopathic tendencies were less likely to yawn when they saw someone else yawning."