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"How much did Santa's sleigh cost? Zero, it was on the house."

This quip is met by moans that echo through a storage facility in the capital.

We're at a joke-testing meeting with a company that produces supplies for social events. Its catalogue features Christmas crackers.

The company's founder grins, nearly apologetically at the joke. But the joke has been selected and will feature in upcoming crackers.

"You measure the joke by the volume of groans and the loudness of the groans around the table," the founder says.

The secret to a great Christmas cracker joke is not the same as a good joke in itself. It is entirely about the context - in this instance, the communal amusement of the holiday dinner table with grandparents, kids and potentially neighbours.

"The goal is for the gag to be something that brings the eight-year-old together with the grandparent," she states.

The Science Of Communal Laughter

Coming together to enjoy shared amusement is not only nothing new, experts argue, it is likely to be pre-human.

"So when you are chuckling with people around the Christmas dinner you are dropping into what's very likely a truly ancient mammalian play vocalisation," explains a neuroscience expert.

Communal laughter, she explains, aids in forge and strengthen social bonds between people.

Scientists have found that a lack of these social exchanges can seriously harm mental and physical well-being.

"Those you converse with, and share laughter with, it leads to increased levels of endorphin release," she continues.

These natural chemicals are the brain's "feel-good compounds" and are released both to alleviate stress and pain and in response to pleasurable experiences, such as laughing with loved ones over a particularly awful festive cracker gag.

"You're not just chuckling at a foolish joke with a holiday cracker," she states. "You are actually performing a lot of the truly vital task of making, maintaining the connections you have with the people you love."

What Happens Inside the Mind?

But what is truly taking place inside the brain when we listen to a gag?

An awful lot happens in reaction to humour, it transpires.

Employing functional magnetic resonance imaging (fMRI), a kind of neural imager which indicates which parts of the brain are working harder, scientists have been able to chart the regions that receive more blood.

The research involves imaging the brains of volunteer participants and then subjecting them to a database of funny words, paired with either a non-emotional sound, or pre-recorded chuckles.

"During the study we observed a really fascinating activation pattern of neural activity," notes the professor.

A joke activates not just the parts of the mind responsible for auditory processing and understanding language, but also neural areas associated with both planning and initiating motion and those linked to sight and memory.

Put these elements as a whole, and people listening to a pun have a complex set of brain responses that support the laughter we hear.

The Infectious Nature of Chuckles

Scientists discovered that when a humorous phrase is combined with laughter there is a greater reaction in the mind than the same word when accompanied by a non-emotional sound.

"This activation occurred in areas of the mind that you would use to contort your expression into a grin or a laugh," the professor says.

It indicates we are not just responding to funny jokes, they are reacting to the laughter that accompanies them.

Amusement, says the professor, can be contagious.

So what does this imply for the chuckles found around a holiday table?

"People laugh more when you are familiar with others," she says, "and you laugh further when you like them or love them."

When it comes to festive cracker puns, she says, the positive effect is more likely to be triggered not by the joke itself, but from the response to it.

"The laughter is key. The gag is the terrible Christmas cracker pun, and it's just a reason to chuckle together."

The Search for the Ideal Cracker Joke

Is it possible to find the perfect gag?

Likely not, but that has not prevented experts from trying to.

In 2001, a psychologist established a scientific project for the planet's funniest joke.

More than tens of thousands of jokes later, with ratings provided by 350,000 participants around the world, he has a better understanding than many as to what works and what does not.

The perfect festive cracker pun needs to be brief, he says.

"They must also need to be poor jokes, puns that cause us to moan," he adds.

The increasingly "terrible" the joke, he says the better.

"This is because if no-one laughs – it's the gag's fault, not yours.

"What's interesting about the holiday cracker jokes is that not one person find them humorous.

"It creates a common moment at the table and I think it's wonderful."