Go on. We dare you not to crack a smile when you look at this photobombing squirrel picture.

And there’s a reason it makes you grin – and it’s scientific.

The photo topped a poll by Coca-Cola Great Britain as the happiest photograph, with 71% of people surveyed unable to resist smiling when they see it.

Psychologist Dr Simon Moore explains: “The unexpected element in this shot, and our response to it, may help to explain why photobombing has become such a popular trend – it results in an unexpected emotional experience. Sudden ‘nice’ surprises are good as psychologically we feel we got more than we were expecting.”

Bobby Brittain, Marketing Director, Coca-Cola Great Britain said: "The findings suggest that it’s often small things - like a cute animal or unexpected photo-bomb - that make us feel happy. Our Choose Happiness campaign is all about inspiring people to appreciate the little things that raise a smile. That's why we’re encouraging people to capture whatever makes them happy this summer and giving away up to one million selfie sticks.”

So which other pictures made the grade?

No2: Pretty in pink

This pink-hatted baby proved the biggest small human. It was also voted the ‘most smiled at’ by women.

No 3: What a hoot!

This snowy owl won out over the most socially shared animals – cats and dogs – to make more people smile.

No 4: Tall story

This giraffe image proved irresistible in testing. Its smiling face, framed by blue sky and fluffy clouds promoted a smile from over two-thirds of people.

No 5: Top dog

He certainly looks happy – and his grin triggered a mirror smile in three-quarters of people.

No 6: Cat cuddle

The world’s favourite pets come together in this adorable snap.

No 7: Extreme close-up

What’s not to love about this extreme furry close-up of a quokka?

Which picture makes you the happiest? Tell us in the Comments box below.