Behind the smile

1 Try this simple test. Stand in front of a mirror. Now imagine that a good friend has given you a birthday present but you really don't like it. Try and smile as if you loved it. Look at your smile in the mirror. If someone smiled at you like this, would you know it was false?

2 The truth is, we are surprisingly bad at telling whether the expression on someone's face corresponds to what they are really feeling. If someone looks happy, we tend to believe they are happy. Studies reveal that even experts in lie detection like police officers and psychiatrists find it very hard to tell when someone is lying to them.

3 But this could change, thanks to researchers at San Fransisco University. They have discovered that a false smile not only feels different, it also looks different.What's more, a fake smile is actually controlled by a different part of the brain. In a real smile, a particular muscle around the eye contracts, which causes the skin around the eye to tighten and create lines. When you put on a false smile, this doesn't happen. The researchers say that if you know what you are looking for, a person's face can tell you if they are lying or not.

4 So, could a police officer know a suspect is lying simply by looking at their face? Yes, but not always, say the researchers. Police officers could be trained to interpret facial expressions, they say, but around 10% of the population are what they call "natural liars", and natural liars are almost impossible to catch.