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Ever watch a supposedly contented couple interact and think, "Something's wrong here. I have an odd feeling he is cheating on her"?

Well, newly published research suggests there's a good chance you're right.

"People make remarkably accurate judgments about others in a variety of situations after just a brief exposure to their behavior," writes a research team led by Brigham Young University psychologist Nathaniel Lambert. In the journal Personal Relationships, the researchers provide evidence that this ability extends to infidelity detection.

Lambert and his colleagues describe two studies, the first of which featured 51 university undergraduates (35 women and 16 men), all of whom were in romantic relationships. One member of each couple completed a detailed survey about their relationship, including whether they had been emotionally or physically unfaithful.

Lambert and his colleagues note that the ability to detect cheating makes sense from an evolutionary perspective, "given some of the adverse consequences of infidelity."

"Couples were then instructed to complete a drawing task in which one of the partners was blindfolded, and the other partner gave instructions to the blindfolded participant regarding what to draw," the researchers write.

These videotaped three- to five-minute sessions were watched by six "objective coders" who subsequently answered questions such as "How likely is it that this person flirted or made advances on someone other than the partner?" and "How likely do you think this person has had sexual intercourse with someone other than his/her partner" on a one-to-five scale.

"We found a significant and moderate effect size in the correlation between rater's judgments of infidelity likelihood and (a) participant's actual infidelity," the researchers report.

The second study, featuring 43 undergraduates, was very similarly structured, except that the coders also judged (on a one-to-five scale) how committed each participant was to the relationship, and how trustworthy they seemed.

Once again, the coders identified cheaters at a significantly above-chance level, and their judgments were strongly linked with their perceptions of commitment and trustworthiness. Thus it seems the observers picked up on certain verbal or visual clues that pointed to a certain ambivalence and/or lack of reliability, and this made them justifiably suspicious of the person's fidelity.

“I was personally amazed about what could be surmised about people after watching them on a video for just a few minutes,” said Lambert. “First, I couldn't believe how consistent the observers were with each other at independently rating who they thought were cheating on their romantic partner. Second, I was surprised by how often they were right on the mark.”

Lambert and his colleagues note that the ability to detect cheating makes sense from an evolutionary perspective, "given some of the adverse consequences of infidelity." Of course, if you're looking for a short-term fling, the ability to note a promising target could also come in handy.

So, if your friends have suspicions about your mate, don't dismiss them out of hand. Sure, they may just be jealous. But their casual observations of your interactions with your partner may be providing them with valuable, if painful, insights.