As a student, Elena Kurzius often caught herself imitating a conversation partner's accent or way of speaking. "I felt a little awkward and strange when I noticed myself doing that," she says. Curious, she began researching the tendency, which she soon found had a name: the chameleon effect.

First described in 1999, the chameleon effect refers to the unwilling and unconscious ways that we adapt our behaviors to match those of our partner's. "Although it's everywhere and happening all the time, we hardly notice it," Kurzius says. "I wanted to know why we function this way, because I wanted to characterize myself and find out why I do it."

Now a psychologist at the Martin Luther University of Halle-Wittenberg in Germany, those questions have motivated Kurzius' research ever since. As she and others have discovered, positive behaviors and those that facilitate cooperation—including smiling, laughing and nodding—are the ones most often mimicked. But the chameleon effect may also extend to posture, foot shaking, accents, speech rhythm and more.

Our tendency to mimic likely evolved as a way to help us get along with others. In experiments, people report liking a partner who is mimicking them more than one who is not, and we are also more prone to mimic those we wish to impress or ingratiate. At the same time, the chameleon effect seems to put the mimicker get on a similar mental wavelength as the person whose behaviors she is mirroring. For these reasons, mimicry is sometimes referred to as social glue. "If we're undertaking the same behavior as our interaction partner, it helps us understand what he means and how he feels," Kurzius says. "Additionally, it also makes him feel better and enjoy the interaction more."

While nearly everyone seems to engage in mimicking from time to time, past research shows that some people seem more prone to it than others. Those who are highly empathetic, for example, tend to mimic more. Kurzius, however, wanted to know more about the relationship between broader aspects of personality and mimicry. So she recruited 32 volunteers and told them they would be helping out in a study of morality in fairy tales. After taking a Big Five personality test, Kurzius asked the participants to recount a fairy tale, which she recorded. This provided her with a benchmark of the natural pace of each participant's speech.

Next, she paired the unsuspecting volunteers with actors trained to talk either extra quickly or extra slowly. The volunteers, however, thought the actors were other participants, like them. Kurzius asked the pairs questions about fairy tales, which the actors always answered first.

Based on past research, she expected that people who scored high in extraversion—those who are sociable and talkative—and those who scored high in agreeableness—ones that are good natured, sympathetic and courteous—would be more likely to mimic their partner's talking speed. Her analysis of the recordings and comparison with the personality tests, however, yielded slightly different results.

While extraverts were indeed significantly more susceptible to the chameleon effect, agreeable people were not. On the other hand, people who were open—ones who are creative and curious—did tend to adjust their talking speed to match their partner's.

Kurzius and other experts think that people with extraverted personalities tend to mimic more because they prioritize being liked by others. For them, the chameleon effect is a way, whether consciously or not, to win favor and gain approval.

Why open people might be more prone to the chameleon effect, however, is a trickier question. Kurzius hypothesizes that perhaps their openness to new experiences extends to seeing the world through another person's eyes, which makes them more prone to adopt the mannerisms of those around them.

In a second, similar study, Kurzius dug into whether some people are more prone to certain types of mimicry than others. She found that neurotic individuals—those who are high-strung, nervous and insecure—tend to mimic negative behaviors such as shaking their head, frowning or shrugging significantly more than others, while conscientious and open people tended to do the opposite, largely ignoring negative behaviors. "Different people are prone to imitate different behaviors," she says. "So there's no clear answer like 'These are the people who mimic more or less'—it depends on the behavior."

Unanswered questions still abound, including if and when the effect can backfire. In an as-of-yet unpublished study, Kurzius found that mimicking someone after 10 to 20 seconds passes—rather than within the usual 10 seconds—produces negative results. Instead of gaining favor, the other person begins to dislike the mimicker. And although untested, Kurzius suspects that overkill mimicry would also produce undesired effects. "If I see someone mimicking me all the time, I'd wonder what this guy wants from me and probably wouldn't like him too much," she says. "It's like that game we used to play as children when someone mimics the other, but all the time. After five minutes or so, the other one would get so angry."

Continued exploration of the pluses and pitfalls of the chameleon effect will help us not only better understand human relationships and our own motivations and behaviors, Kurzius says, but also create new therapies for those who have trouble relating and interacting with others.