Two Thai teenagers have discovered laughter isn't always the best medicine after they were arrested for selling balloons containing "funny air" - or laughing gas - to tourists.

London - It’s a social skill we keep up our sleeve for those awkward moments such as a boss’s bad joke or an excruciating wedding speech.

But while we might have perfected the art of the fake laugh, even our most realistic efforts to feign amusement fool no one, according to scientists.

Their research has found people are “extremely good” at distinguishing even the most realistic sounding fake giggles.

It found volunteers could almost always tell the difference between someone genuinely erupting into laughter and what the experts called “social laughter”.

Sophie Scott, professor of cognitive neuroscience at University College London, carried out brain scans on volunteers listening to expressions of disgust, a real belly laugh and a realistic fake one.

The volunteers were almost always able to identify a false laugh, she said.

But Professor Scott, author of the study presented today at the Royal Society Summer Science Exhibition in London, said that while we know if people are only pretending to laugh at our jokes, this is in fact a compliment rather than an insult.

“Most of our laughter is posed,” she said. “We use it as a way of keeping conversation going, as a way of showing our friends we like them or impressing people.

“They know it’s not genuine, but I don’t know if they always mind. You are appreciating what they are doing and getting a positive affiliation going.”

The MRI scans also revealed how hearing real and fake laughter activates two different areas of our brains.

Fake laughter triggers more brain activity – in the medial prefrontal cortex, associated with problem-solving – as we try to work out why the person is doing it. Genuine laughter simply activates auditory areas in the temporal lobe – where we process all sound. - Daily Mail