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

This quip is greeted with groans that echo through a storage facility in the capital.

This describes a joke-testing session with a firm that makes supplies for gatherings. Its catalogue includes Christmas crackers.

The firm's owner smiles, almost apologetically at the joke. But the pun has made the cut and will feature in future crackers.

"You measure the joke by the volume of moans and the loudness of the groans at the table," she says.

The secret to a good holiday cracker pun is not the identical as a stand-up joke in itself. It is all about the setting - in this instance, the communal laughter of the holiday dinner table with grandparents, kids and potentially neighbours.

"The goal is for the gag to be a thing that unites the eight-year-old together with the grandparent," she adds.

The Neuroscience Of Shared Laughter

Coming together to enjoy communal amusement is not only nothing new, experts argue, it is probably to be older than humanity.

"Therefore when you are laughing with people around the holiday dinner you are engaging in what's almost certainly a really ancient mammalian social sound," says a neuroscience expert.

Shared laughter, she says, aids in make and maintain social bonds between individuals.

Researchers have discovered that a lack of such interactions can seriously damage both psychological and bodily health.

"The people you converse with, and share laughter with, it leads to increased levels of endorphin uptake," the professor adds.

These natural chemicals are the body'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 terrible festive cracker gag.

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

Which Occurs Inside the Brain?

But what is actually happening within the brain when we listen to a gag?

A tremendous amount occurs in response to humour, it turns out.

Employing functional magnetic resonance imaging (fMRI), a kind of brain scanner which shows which areas of the brain are working harder, researchers have been able to chart the regions that get more blood flow.

The research entails imaging the brains of volunteer subjects and then exposing them to a database of humorous phrases, paired with either a non-emotional sound, or recorded chuckles.

"During the study we observed a very interesting pattern of neural activity," notes the professor.

A gag stimulates not just the areas of the mind in charge of hearing and interpreting speech, but also neural areas involved in both planning and initiating movement and those involved in vision and recall.

Combine these elements as a whole, and people listening to a pun have a sophisticated set of brain reactions that support the laughter we experience.

The Infectious Power of Chuckles

Scientists found that when a funny word is combined with laughter there is a stronger response in the brain than the identical word when followed by a neutral sound.

"This was in areas of the brain that you would employ to contort your face into a grin or a laugh," the professor explains.

It means people are not just responding to humorous jokes, they are responding to the laughter that accompanies them.

Laughter, says the professor, can be contagious.

So what does this mean for the chuckles heard at a Christmas gathering?

"You laugh more when you are familiar with people," she says, "and laughter increases more when you like them or care for them."

When it comes to festive cracker puns, she says, the feel-good effect is more probable to be triggered not by the gag in itself, but from the response to it.

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

The Search for the Perfect Festive Pun

Is it possible to discover the perfect joke?

Probably not, but that has not prevented researchers from trying to.

Years ago, a psychologist set up a scientific search for the planet's most humorous gag.

Over tens of thousands of jokes submitted, with ratings lodged by hundreds of thousands of participants around the world, he has a better idea than most as to what succeeds and what does not.

The ideal festive cracker joke needs to be short, he explains.

"But they also need to be poor jokes, jokes that cause us to moan," he continues.

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

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

"What's interesting about the Christmas cracker puns is that none of us considers them humorous.

"It creates a shared moment around the table and I believe it's lovely."