A 2016 review of studies, published in the journal Aggression and Violent Behavior and highlighted on Inc., found that psychopaths tend to speak slowly and control their speech more so than non-psychopaths.
They also use fewer emotional words, keeping a relatively neutral tone.
Psychopaths tend to use more past-tense verbs
That's according to the 2016 review.
Researchers suspect this is because they're more psychologically and emotionally detached from the conversation topics.
Psychopaths tend to use emotional language without displaying much feeling
Psychopaths' language tends to lack what psychologists call an "emotional dimension," according to the 2016 review.
From the paper: "A psychopath can say, 'I love you,' without feeling anything else than asking for a cup of coffee."
Narcissists tend to use more offensive language
A 2014 study published in the journal Personality and Individual Differences suggests that's likely because narcissists see offensive language as attention-grabbing and because they're less sensitive to the offensiveness.
Narcissists tend to display exaggerated body language and facial expressions
The 1990 study on conversational narcissism also found that narcissists tend to be overly dramatic in their hand gestures and facial expressions.
They may also speak in a loud tone of voice.
Psychopaths and narcissists tend to tell the same fabricated stories over and over again
A blog post on Psychology Today suggests that narcissists and psychopaths both tend to repeat "confidential" information they've previously shared.
The editors who wrote the post say narcissists and psychopaths often use scripted lies: "Because people are interchangeable in the eyes of a psychopath or a narcissist—one-dimensional beings in whom they have no genuine interest—it can be hard for them to remember what they've said, and to whom."