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"What was the price did Santa's sleigh cost? Nothing, it was on the house."

This one-liner is met by groans that echo through a warehouse in the capital.

We're at a joke-testing session with a company that produces supplies for gatherings. Its repertoire features Christmas crackers.

The company's owner smiles, nearly apologetically at the gag. But the pun has been selected and will feature in future crackers.

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

The secret to a great Christmas cracker joke is not the same as a stand-up joke per se. It is all about the setting - in this case, the communal amusement 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 in harmony with the grandparent," she adds.

The Neuroscience Of Communal Amusement

Coming together to experience shared laughter is not only ancient, experts argue, it is probably to be pre-human.

"Therefore when you are chuckling with people at the Christmas dinner you are engaging in what's very likely a really primordial mammalian social sound," explains a neuroscience expert.

Shared amusement, she says, helps forge and strengthen social bonds between people.

Researchers have found that a lack of these social exchanges can seriously damage mental and physical health.

"The people you talk to, and share laughter with, it results in increased levels of 'happy chemical' uptake," she continues.

Endorphins are the brain's "happy chemicals" and are released both to alleviate stress and pain and in reaction to enjoyable activities, such as laughing with loved ones over a truly awful Christmas cracker joke.

"It's not simply chuckling at a silly joke with a holiday cracker," the expert says. "You are actually doing a lot of the really important task of making, maintaining the connections you have with the people you love."

Which Occurs In the Mind?

But what is truly happening within the mind when we hear a gag?

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

Using brain scanning technology, a type of neural imager which shows which parts of the mind are working harder, researchers have been able to chart the regions that get more blood flow.

Testing involves scanning the minds of healthy participants and then subjecting them to a collection of funny phrases, accompanied by either a neutral sound, or recorded laughter.

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

A gag activates not just the parts of the brain responsible for hearing and interpreting speech, but also brain regions involved in both planning and initiating movement and those involved in sight and memory.

Put all of this as a whole, and people listening to a joke have a sophisticated series of brain reactions that support the laughter we experience.

The Contagious Power of Chuckles

Researchers discovered that when a humorous phrase is combined with laughter there is a greater response in the mind than the identical word when followed by a neutral sound.

"This was in areas of the mind that you would use to contort your face into a grin or a laugh," she says.

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

Laughter, according to the professor, can be contagious.

So what does this imply for the chuckles found at a holiday gathering?

"You laugh more when you know people," she notes, "and laughter increases further when you are fond of them or care for them."

When it comes to Christmas cracker puns, she says, the positive factor is more likely to be caused not by the gag in itself, but from the reaction to it.

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

The Search for the Perfect Festive Pun

Will we ever find the perfect gag?

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

Years ago, a professor set up a research project for the world's most humorous joke.

Over tens of thousands of jokes later, with ratings provided by 350,000 people around the world, he has a clearer idea than most as to what succeeds and what fails.

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

"But they also be poor gags, puns that make us groan," he adds.

The increasingly "awful" the gag, he says the better.

"The reason is that if no-one laughs – it's the gag's shortcoming, not your own.

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

"That's a common experience around the table and I think it's lovely."