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"What was the price did Santa's sled cost? Zero, it was on the house."

This joke is met by groans that echo through a warehouse in the capital.

We're at a joke-testing session with a firm that makes supplies for gatherings. Its repertoire includes festive crackers.

The company's founder grins, almost apologetically at the gag. But the pun has been selected and will feature in future crackers.

"The success is gauged by the joke by the volume of groans and the intensity of the groans around the table," the founder says.

The secret to a good Christmas cracker joke is not the same as a good joke in itself. It is all about the context - in this case, the shared amusement of the holiday meal with grandparents, children and possibly friends.

"You want the gag to be a thing that brings the eight-year-old together with the grandparent," she adds.

The Neuroscience Of Shared Laughter

Gathering to experience communal amusement is not only ancient, scientists argue, it is likely to be pre-human.

"Therefore when you are laughing with others at the holiday table you are engaging in what's very likely a truly primordial mammal social vocalisation," explains a professor.

Communal laughter, she says, aids in forge and strengthen social connections between people.

Researchers have discovered that a absence of these interactions can significantly harm both psychological and bodily well-being.

"Those you converse with, and share laughter with, it results in increased amounts of endorphin uptake," the professor continues.

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

"You're not just chuckling at a silly pun with a Christmas cracker," she says. "You are in fact doing a lot of the really important task of building, preserving the social bonds you have with those you love."

Which Occurs Inside the Brain?

But what is actually happening inside the brain when we hear a joke?

An awful lot happens in response to comedy, it turns out.

Employing functional magnetic resonance imaging (fMRI), a type of neural imager which indicates which areas of the mind are more active, researchers have been able to map the regions that get more blood flow.

The research involves scanning the minds of volunteer participants and then exposing them to a database of funny phrases, accompanied by either a neutral sound, or recorded laughter.

"In the scanner we observed a really fascinating activation pattern of activation," says the neuroscientist.

A joke stimulates not just the areas of the brain responsible for hearing and interpreting speech, but also brain regions associated with both planning and starting motion and those involved in sight and memory.

Combine all of this together, and individuals hearing a joke have a sophisticated set of brain responses that underpin the laughter we experience.

The Infectious Nature of Chuckles

Researchers found that when a funny word is combined with laughter there is a stronger reaction in the mind than the same word when accompanied by a neutral sound.

"This was in parts of the brain that you would use to move your expression into a grin or a laugh," she says.

It means people are not just responding to funny words, they are responding to the amusement that accompanies them.

Amusement, according to the professor, can be contagious.

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

"You laugh more when you know people," she notes, "and laughter increases further when you like them or love them."

When it comes to festive cracker jokes, she explains, the feel-good effect is more likely to be caused not by the joke in itself, but from the reaction to it.

"It's the laughter. The gag is the terrible holiday cracker joke, and it's just a reason to laugh together."

The Quest for the Ideal Cracker Joke

Is it possible to find the perfect joke?

Likely not, but that has not stopped researchers from attempting to.

In 2001, a psychologist set up a scientific project for the planet's funniest gag.

More than tens of thousands of jokes submitted, with ratings lodged by 350,000 participants globally, he has a better idea than most as to what succeeds and what fails.

The ideal festive cracker joke must be short, he explains.

"But they also be bad jokes, jokes that cause us to moan," he adds.

The more "terrible" the gag, he states the more effective.

"This is because if nobody laughs – it's the joke's shortcoming, not yours.

"The fascinating part about the Christmas cracker jokes is that none of us considers them funny.

"It creates a common moment around the gathering and I believe it's lovely."