It’s considered mannerly to do whenever singing the national anthem or reciting the Pledge of Allegiance — putting your hand over your heart, that is. But according to a new study, it can actually make you seem more trustworthy to others and compel you to tell the truth.

Researchers Michal Parzuchowski and Bogdan Wojciszke of the University of Social Sciences and Humanities in Sopot, Poland, said in the Journal of Nonverbal Behavior that people were more likely to tell the truth when they had their hand on their heart. The researchers also believe a similar effect happens when people raise their right hang to take an oath. "Four studies demonstrated that the emblematic gesture associated with honesty (putting a hand on one’s heart) increased the level of honesty perceived by others, and increased the honesty shown in one’s own behavior," the team wrote. This might seem like a no-brainer since placing a hand over one's heart is used when trying to express honesty.

The second experiment had 37 university students who listened to parts of an audio recording of a job interview. The applicants say statements like, “I have never been late for work” and “I have never even argued with members of my family.” They listened to students, looked at photographs of the speakers, and were asked to rate which one they believed more — the one with the hand over his heart or the one without. Almost all of the students believed the person with his hand over his heart more.

In the third experiment, 48 students were asked to rate the looks of women. “When presented with an opportunity to lie about someone’s appearance, people who put their hands over their hearts remained more honest, even if it meant being impolite,” the authors wrote.

In the last experiment, 52 students solved math problems and 17 wrote down the solutions. The others had their dominate hand occupied with a different unrevealed activity, and they had to “remember the number of solved problems and report them.”

The basis of these experiments just show that placing our hand over our hearts might compel us to behave more morally. This does, however, open up another issue for skilled liars; they could use this technique to manipulate other people into believing what they are saying. This is why Parzuchowski and Wojciszke warn that a simple gesture like this one should not be taken as a "truth serum."

Source: Parzuchowski M, Wojciszke B. Hand over Heart Primes Moral Judgments and Behavior. Journal of Nonverbal Behavior. 2013.