Anna Mecagni didn't know Portuguese when she traveled through Brazil, so she had to improvise. Her fluent Spanish was enough to get a conversation started but practically useless when it came to comprehending the response. So the business student from Los Angeles opted to use the international language (or so she thought) of gestures-shrugging shoulders, cocking eyebrows, nodding her head and talking with her hands. She had the last word every time she flashed the okay sign. Brazilians consider the Rodney Dangerfield-trademark circled thumb and forefinger a vulgar reference to the female anatomy. Mecagni had to fumble her way through more than a few apologies once she realized the error of her ways.

The lesson: Never assume that the routine body language of home will be universally understood. In countries like Brazil (and Russia and Germany, where the okay sign translates simply to 'you asshole'), an innocent, misdirected digit can lead to an instant communication breakdown, red faces and floods of foreign invective. 'As an American, you get so used to flashing the okay sign, it's hard to interpret it any other way,' Mecagni explains. 'It got to the point where I had to physically restrain my impulse to do it.'

That reflexive urge is hard to resist. Researchers say 90 percent of our emotions are expressed without uttering a single word. Apparently we wear our hearts not only on our sleeves, but everywhere else, too. 'Gestures are woven inextricably into our social lives,' maintains Roger Axtell in Gestures: The Do's and Taboos of Body Language Around the World. 'Both individuals and groups still send vital messages by gesture, by pantomime, by dramatics-by a dizzy diversity of what scholars call nonverbal communications.'

These signals can be powerful emotional triggers, causing friends to come to blows, creating friendships among strangers, evoking passion in the apathetic and conveying hidden intentions without a word spoken. Axtell cites the example of a young Western hitchhiker in Nigeria who was roughed up by a passing crew of motorists who took offense at his upturned thumb, an extremely rude gesture in those parts. Down Under, an American couple's appreciative thumbs-up to a highway officer who decided not to fine them for a moving violation provoked a severe backlash-a litany of curses and a stiff penalty. The couple had signaled 'screw you' with a vertical up-yours thumb.