Real psychopaths don’t giggle.

The maniacal laugh: only in the movies. For a more realistic psychopath, look to bolt-gun–wielding Anton Chigurh from No Country for Old Men. He just quietly walks up and it’s ka-chunk, you’re dead.

That’s the diagnosis from forensic psychiatrist Samuel Leistedt, who has interviewed and diagnosed real psychopaths, people who he describes as feeling no empathy for others. “They’re cold-blooded,” he says. “They don’t know what an emotion is.”

Leistedt and his colleague Paul Linkowski spent three years watching 400 movies looking for realistic portrayals of psychopaths. Leistedt says he personally watched all 400, some several times. That means he not only watched Psycho, but sat through Pootie Tang in the name of science.

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He first weeded out clearly unrealistic characters, such as those with magic powers or who were invincible or not human (such as ghosts). That whittled it down to 126 films from 1915 to 2010, showing 105 male and 21 female potential psychopaths. A team of about 10 forensic psychiatrists and movie critics watched and weighed in on diagnoses.

They did this to develop tools for teaching psychiatry students, and ended up tracing a social history of how psychopaths have been viewed and understood since the early 20th century. Learning to diagnose a psychopath is not easy, he says. Not only are definitions and traits of psychopathy disputed, but students get limited chances to interview psychopaths.

Psychiatrists and neuroscientists have identified behavioral characteristics of psychopaths and parts of the brain that appear to function differently than in the average person. But much remains unknown; experts still disagree about whether and when there’s a genetic basis for psychopathy. Hollywood images of psychopaths have shifted over time as this understanding has changed, and as real-life cases came to light from serial killer Ed Gein to Ted Bundy and Jeffrey Dahmer.

Overall, portrayals have gotten more realistic over time, Leistedt and Linkowski report in the January Journal of Forensic Sciences. Instead of giggling killers with facial tics, at least a few of today’s portrayals have more depth, giving a “compelling glimpse into the complex human psyche,” they write.

Here are a few of the best and worst potrayals from Leistedt and Linkowski’s paper.

The frighteningly realistic:

1. Anton Chigurh, No Country for Old Men (2007)

This contract killer hauls around a bolt pistol attached to tank of compressed air, a handy tool both for shooting out door locks and for shooting people in the head. Leistedt says Chigurh is his favorite portrayal of a psychopath. “He does his job and he can sleep without any problems.In my practice I have met a few people like this,” he says. In particular, Chigurh reminds him of two real-life professional hit men who he interviewed. “They were like this: cold, smart, no guilt, no anxiety, no depression.”

Diagnosis*: Primary, classic/idiopathic psychopath

2. Hans Beckert, M (1931)

This child-murdering character broke with most portrayals of psychopaths at the time, depicting an outwardly normal man with a compulsion to kill. This is “a substantially more realistic depiction of what would eventually be known today as a sexually violent predator most likely suffering from psychosis,” Leistedt and Linkowski write.

Diagnosis: Secondary, pseudopsychopath, additional diagnosis of psychosis

In this film about guy who likes to find new ways to kill people, the researchers write, “the main, interesting theme is the chaos and instability in the life of the psychopath, Henry’s lack of insight, a powerful lack of empathy, emotional poverty, and a well-illustrated failure to plan ahead.”

Diagnosis: Primary, classic/idiopathic psychopath

Scary, but not realistic:

1. Tommy Udo, Kiss of Death (1947)

A great example of an early portrayal of a “madman” as psychopath. The Udo character was famous for his creepy chuckle, and legend has it that actor Richard Widmark was later asked repeatedly to record the laugh on blank record albums.

2. Norman Bates, Psycho (1960)

After the 1957 arrest of real-life serial killer Ed Gein, a case involving cannibalism, necrophilia and a troubled relationship with his mother, horror films about serial murder took off. Norman Bates was inspired in part by Gein, launching a genre showing misfits with usually sexual motivations to kill. This kind of behavior became closely linked to psychopathy, but Gein was more likely psychotic, meaning out of touch with reality. Psychosis, which is a completely different diagnosis from psychopathy, often involves delusions and hallucinations.

3. Hannibal Lecter, Silence of the Lambs (1991)

Yes, he scares the bejesus out of me, too. But Lecter’s almost superhuman intelligence and cunning are just not typical among, well, anyone, let alone psychopaths. Lecter is a perfect example of the “elite psychopath” that became popular in the 1980s and 1990s. This calm, in-control character type has sophisticated tastes and manners (think Chianti and jazz),exceptional skill in killing and a vain and “almost catlike demeanor,” the researchers write, adding, “These traits, especially in combination, are generally not present in real psychopaths.”

The new release The Wolf of Wall Street may be part of another movie-psychopath trend, the “successful psychopath.” Leistedt hasn’t seen the film yet, but he says the story of real-life con man Jordan Belfort should make for an interesting portrayal. “These guys are greedy, manipulative, they lie, but they’re not physically aggressive,” Leistedt says. Gordon Gekko in Wall Street is an example of a realistic successful movie psychopath. He’s “probably one of the most interesting, manipulative, psychopathic fictional characters to date,” the researchers write.

Hollywood has lately been fascinated by these successful psychopaths, Leistedt and Linkowski note, in the wake of financial crises and high-profile trials such as Bernard Madoff’s. Apparently, vicious stockbrokers are the new bogeymen. Instead of disemboweling their victims, they gut their bank accounts.

No matter the subtype, one thing is clear: Psychopaths are the people we meet in our nightmares. And sometimes in the boardroom. We’re fascinated and repelled by them, so it’s no surprise that they are the subject of so many of our favorite films.

*The diagnoses of characters in Leistedt and Linkowski’s study are based on classifications outlined by forensic psychologist Hugues Hervé and by psychiatrist Benjamin Karpman. Definitions vary, and the descriptions below are general guidelines.

Primary versus secondary psychopathy: Primary psychopaths are deficient in affect, or emotion, from birth, suggesting a genetic basis. They are often described as more aggressive and impulsive. Secondary psychopaths have been shaped by their environment, may have had an abusive childhood, and are often described as having more fear and anxiety than primary psychopaths. ‘’

Subtypes:

classic/idiopathic Score the highest on all sections of the widely used Hare Psychopathy Checklist, or PCL-R, showing low fear, lack of inhibition and lack of empathy.

manipulative Tend to be good “talkers” and associated with crimes involving fraud.

macho Lack the glibness and charm of the above groups but manipulate through force and intimidation.

pseudopsychopaths Also called sociopaths; show antisocial behavior but score lowest among these groups on the PCL-R.