Next time your teacher tells a bad joke and you feel compelled to laugh, beware – they can tell you’re faking it.

Researchers from London have discovered our brains carry out different process when we hear genuine laughter compared to fake chuckles.

When laughter is forced, for example, it activates a part of the brain linked with deciphering emotions.

This means we know it’s not a genuine laugh, and we automatically try to work out why they’re faking it, what the laugh means and what the they’re thinking.

While genuine laughter lights up areas of the brain linked with happiness and positive emotions.

To test the theory, psychologist Dr Carolyn McGettigan from the Royal Holloway University of London measured brain responses of volunteers as they listened to genuine laughter on YouTube clips.

The results were then compared to how their brains responded to fake laughter.

The findings revealed participants, none of which were told the study was about laughter perception, could unconsciously tell when the chuckles were insincere.

Dr McGettigan said: ‘It’s fascinating to consider the way our brain is able to detect genuine happiness in other people. ‘Our brains are very sensitive to the social and emotional significance of laughter.

The study goes a long way to explain why people can easily spot when someone is forcing laughter.

‘This suggests that as listeners, ‘trying out’ how a laugh would feel if we produced it ourselves might be a useful mechanism for understanding its meaning.’