The truth, according to the popular television show "Lie to Me," is "written all over our faces," but psychologists say that visual clues are only one part of the way humans read each other's emotions.
Just this week, police released the 911 tape and radio dispatches of the arrest of Harvard professor Henry Louis Gates Jr., trying to unravel whether -- in Obama's words -- the police department reacted "stupidly."
Emotions ran high in all camps, including the White House, where Obama revealed what psychologists call "non-verbal leakage."
The president's pursed lips were caught on camera as he came short of issuing an apology, inviting Cambridge, Mass., Sgt. James Crowley to talk things out over a beer.
A big part of Obama's ability to exude success has been his body language, according to expert T.J. Walker, who preps world leaders, journalists and businesspeople on public speaking, "making sure facial expressions are in sync."
"I think Obama was disappointed in himself that he got sucked into this," said Walker, CEO of Media Training Worldwide. "It's so rare that he does stumble into something. Compared to the last four presidents, he gets off message and sticks his foot in his mouth less often."
This is not the first time Obama has been caught with a grimace. He has more than once non-verbally chastised a blundering Vice President Joe Biden with a dagger glance.
Boston College professor and lying specialist Joseph Tecce has used his expertise in reading emotion to accurately predict national election results, though he admits the 2000 presidential race eluded his call.
"Obama generally has a gaze aversion habit," he told ABCNews.com. "He looks down a lot."
In most instances, according to Tecce, gaze aversion means the person is shy, intimidated by oncoming "verbal repartee," or lying.
Tecce predicted that Obama would win in 2008 because he blinked less frequently -- 62 times a minute -- than Republican candidate John McCain, who batted 104 times in a minute.
"There's a close connection between fast blinking and discomfort, psychologically or physically," he said.
Tecce said Democratic candidate Al Gore would win the popular vote over Republican George W. Bush -- "a fast blinker." He was right in that Gore did win more votes, but the Supreme Court decided the race in favor of Bush.
Other fast blinkers are Roger Clemens, when he testified in Congress on steroid use and O.J. Simpson, according to Tecce, who said lip pursing also raises a "red flag."
Law enforcement has long assessed non-verbal behavior when interrogating suspects.
"It's more of an art than a science," said former FBI profiler Brad Garrett, who is a consultant for ABCNews.com.
Lip tightening is usually read as "trying to control their speech or are getting angry," he said. "It makes sense that someone as cool as Obama was probably pissed that he used that one word [stupidly] and that the press made such a big deal out of it."
Crime suspects [and others] bite, gnaw, cover their mouths, put folders over their faces -- all as an "obstruction," according to Garrett.
"The most important thing about non-verbal behavior is you cannot control it," he said. "What you do you say non-verbally is always going to catch what's really going on inside of you. You turn white, red, your blood pressure is going up and down."