What do you make of a neighbor who’s married, has kids, dresses in a suit daily, rarely misses a day of work, has a well-groomed lawn and a tidy home, is friendly and polite, always asks about your day and your children, and even shovels your snow when you’re out of town? Most people would think this is the best neighbor on the block.

So you may be surprised to learn that this very neighbor “was a sexual sadist who was using a small trailer in this backyard as a torture chamber,” write Mary Ellen O’Toole and Alisa Bowman in their book Dangerous Instincts: How Gut Instincts Betray Us. O’Toole, a retired FBI profiler, worked the case and interviewed the 60-year-old park ranger David Parker Ray, who appeared charming and even seemed to admire women. As it turned out, he’d been torturing women in his backyard for years, and none of his neighbors ever suspected him to be anything but a “regular guy.”

When we try to determine whether someone is a good person or a potential threat, we tend to focus on superficial qualities that actually don’t tell us much about the individual. We assume that people who go to work every day, have a family and a well-kept home are normal—and we give them a lot of credibility, O’Toole said.

We also assume that our bodies will warn us when we’re around someone dangerous. We’ll experience the sensations of fear and know to stay away. But as O’Toole said, dangerous people have a way of making us feel very comfortable. For instance, they’re friendly and courteous and make good eye contact. When O’Toole first saw David Parker Ray, he took her hand and told her how nice it was to meet her. He also was polite and well-mannered. Even O’Toole, who’s worked on the most notorious criminal cases, had to keep reminding herself of his heinous crimes.

What also complicates our ability to read people accurately is that many of us aren’t good listeners. The best way to tell if someone is dangerous is by observing their behavior, O’Toole said. That’s what FBI profilers do. “In order to be a good reader of behavior, you have to watch and listen,” O’Toole said. But if you’re too busy talking the whole time, you may miss key pieces of information.

We also tend to admire and even get intimidated by people in certain professions and positions, which additionally hampers our judgment. O’Toole calls this “icon-intimidation.” We automatically give people a pass if they’re a religious figure, police officer or military person. We assign admirable qualities to them without much thought. We assume they’re intelligent, courageous, compassionate and thereby harmless.

O’Toole gave the example of a recent case in Washington D.C. The area offers a free carpooling service called Slugging, where people give strangers a ride into the city. Last year two commuters got into a pricey car with a retired high-ranking military officer. After they got in, he started driving 90 mph. The people were terrified and insisted on being let out of the car. Once out, one of the people tried to take a picture of his license plate. He tried to run them over.

When reading others, people also “are clouded by their own emotional state,” O’Toole said. Being depressed or just losing a loved one puts you in a vulnerable state when someone offers to do something nice for you, she said.

In our society, we also hold onto many myths that put us in danger. O’Toole calls one of the most common myths “the myth of the straggly-haired stranger.” That is, we think that dangerous people look creepy, unkempt, are unemployed and uneducated and basically stick out like sore thumbs. So we overlook people who may be incredibly dangerous because they look like the rest of us.

Another myth is that good people just snap and act violently, O’Toole said. However, individuals who “snap” already have traits that predispose them to violence, such as a short fuse or physical aggression. It’s more likely, she added, that people minimize the presence of these red flags and that’s why it seems so unexpected.

In fact, it’s common for people to minimize danger in general. We may choose to ignore certain patterns of behavior, rationalize them, explain them away or talk ourselves out of taking action, O’Toole said. Take the example of a couple where one partner becomes increasingly obsessive and jealous (and even physically abusive), which O’Toole commonly sees as a consultant to schools and universities. The young woman wants to end the relationship, but she’s afraid of him. He has many good friends, plays competitive sports and comes from a well-to-do family. She doesn’t want to get him in trouble and worries that their friends will hate her. So the parents decide to deal with the situation on their own. They underestimate the danger. But these are criminal behaviors and they don’t just begin in young adulthood, O’Toole said. It’s likely he’s done similar things with other girls and has other concerning traits. Just getting your daughter out of this situation is not enough, and it “could cause your daughter to lose her life.”

Red Flags When Reading People

Again, reading people accurately means going beyond superficial traits and observing their behaviors. According to O’Toole, these are several red flags of concerning or dangerous actions.

They anger easily or talk about violence.

A person who has a short fuse in one situation will usually have it in another. For instance, if a person has road rage, it’s a good indicator that they also have anger problems outside the car, O’Toole said. Another red flag is if they think that “violence is the answer to everything no matter what they’re talking about.”

They are physically aggressive or abusive to others.

Has the person ever been physically aggressive with you or others? How do they treat staff or servers at a restaurant? If they mistreat others or act like a bully, this likely spills over into other areas of their life, O’Toole said.

They tend to blame others.

Let’s say you’re on your first or second date with a person, and they mention their past relationships. They not only have nothing good to say about their previous partners, but they blame them for everything, she said.

They lack empathy or compassion.

O’Toole views a lack of empathy and compassion as important indicators of someone’s character and their dangerousness. You can identify whether someone is empathetic or compassionate in a simple conversation, and in as little as 10 minutes, O’Toole said. These individuals highjack conversations by interrupting and refocusing the talk back to them.

Again, take the example of a blind date. The person not only blames their past partners for everything, but they may speak harshly about them or even make fun of their physical appearance, O’Toole said.

Psychopaths, who make up about one percent of the general population and 10 percent of prisoners, also lack empathy (among meeting other criteria). They may pretend as though they care, empathize and have feelings for their victims. But, as O’Toole and Bowman write in Dangerous Instincts, “Asking a psychopath what remorse or guilt feels like is like asking a man what it feels like to be pregnant. It is an experience they have never had.” If you keep asking a psychopath about their feelings (such as “How do you feel about those victims?”), they’ll become irritated, and their façade will start to crack, O’Toole said. For psychopaths, “emotions are a pain in their rear end.” They see them as problems, not something worth having.

Reading people accurately isn’t a gift; it’s a skill that anyone can master if they start paying attention to the right things.