From the moment he steps onscreen in the 1960 thriller Psycho, Norman Bates gives audiences the goosebumps. The hotel manager-turned-serial killer just seems, well, off, maybe because he's trying so hard to appear normal. Now a new study suggests that people who fail to appropriately imitate the mannerisms of others during social interactions can actually make their peers feel colder—like Bates, they send a literal chill down the spine.

In most cases, a little bit of imitation is a good thing, says study co-author Pontus Leander, a social psychologist at the University of Groningen in the Netherlands. Friends frequently copy speech patterns and body language, a type of imitation called behavioral mimicry. Psychologists suspect that this behavior, which usually goes unnoticed by either party, can help to build trust. Leander even catches himself slipping into mimicry on occasion. He recently, for instance, moved from North Carolina to the Netherlands and began unwittingly adopting his colleagues' Dutch accents during chats.

But such behavior may not be appropriate in all situations, Leander says. Researchers recently showed, for instance, that when people in leadership roles parrot their subordinates, the underlings became mentally exhausted—a sign that their minds were working overtime to take in the odd behavior. No one expects a stern boss to suck up to them, Leander explains, and when that happens, "it can be weird."

To find out just how that weirdness might feel, Leander and colleagues designed a simple test. An experimenter separately interviewed 40 college undergraduates, subtly tweaking her behavior from person to person. In some cases she acted chummy, dropping words like "awesome" into the conversation. In others, she was much more formal. At the same time, the interrogator alternated between mimicking the students' body language—slouching when they slouched or fidgeting when they fidgeted—and avoiding mimicking entirely.

The students then filled out a survey designed to discover how cold or warm they felt. It may sound strange, Leander says, but people often begin to feel cold when their social lives turn uncomfortable or otherwise unfulfilling—they literally get the chills. Individuals that describe themselves as lonely, for instance, take more frequent hot showers than their peers. And, sure enough, the students in the study reported that they felt colder when the experimenter's social cues seemed somehow off—that is, when she was either acting friendly but not mimicking or seemed professional and did mimic—as the group will report in an upcoming issue of Psychological Science.

The students could hardly be blamed for getting the willies, Leander says. By acting congenial or not, the experimenter had set up basic expectations for the interview: in some cases, "I want to be friends," and in others, "I'd rather keep this professional." Her body language, however, sent the exact opposite message. On an instinctual level, such a deviation from social norms can feel awkward—or downright creepy. "You can feel in your gut that it's not a good thing," he says. It's a good reminder of just how much humans are swayed by reactions that they're not consciously aware of.

"I was very, very impressed," says Eli Finkel, a social psychologist at Northwestern University in Evanston, Illinois. The study, he notes, effectively combines several hot research topics, from behavioral mimicry to embodied cognition, the idea that humans can feel their emotions in very physical ways. William Maddux, a social psychologist at the business school INSEAD in Paris, agrees. The study, he says, highlights that "social norms are really critical to follow in order to establish a good bond with people." He adds that while people can consciously use mimicry to get in good with certain associates, they should proceed cautiously: "You can't do it too much, otherwise people are going to notice."

And they might just think you're a bit psycho.