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

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

We're at a humor-evaluation meeting with a company that produces supplies for gatherings. Its catalogue includes festive crackers.

The company's founder grins, almost apologetically at the gag. But the joke has made the cut and will feature in future crackers.

"You measure the gag by the volume of moans and the intensity of the groans around the table," the founder explains.

The key to a good holiday cracker pun is not the identical as a stand-up joke per se. It is all about the setting - in this instance, the communal laughter of the Christmas meal with elders, kids and potentially friends.

"The goal is for the joke to be something that brings the child together with the 80-year-old," she adds.

The Neuroscience Behind Shared Laughter

Gathering to experience communal amusement is not only nothing new, scientists argue, it is likely to be pre-human.

"Therefore when you are laughing with others around the holiday table you are dropping into what's almost certainly a really primordial mammal play vocalisation," says a neuroscience expert.

Shared amusement, she says, helps make and maintain social connections between individuals.

Scientists have found that a lack of such social exchanges can seriously damage both psychological and bodily health.

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

These natural chemicals are the brain's "happy chemicals" and are produced both to alleviate stress and pain and in response to pleasurable experiences, such as chuckling with friends over a truly terrible Christmas cracker joke.

"You're not just chuckling at a silly joke with a holiday cracker," she states. "You are in fact performing a lot of the really important work of making, maintaining the social bonds you have with the people you care about."

What Happens Inside the Mind?

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

A tremendous amount occurs in reaction to comedy, it transpires.

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

The research entails imaging the minds of healthy participants and then subjecting them to a database of humorous words, accompanied by either a neutral sound, or pre-recorded laughter.

"In the scanner we observed a very fascinating activation pattern of neural activity," says the professor.

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

Combine all of this together, and people listening to a pun have a complex series of brain reactions that underpin the laughter we experience.

The Infectious Power of Chuckles

Scientists found that when a funny phrase is paired with chuckles there is a greater reaction in the mind than the same word when followed by a neutral sound.

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

It indicates we are not just responding to funny words, they are responding to the amusement that follows them.

Amusement, according to the expert, can be infectious.

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

"You laugh harder when you know others," she says, "and laughter increases more when you like them or love them."

When it comes to Christmas cracker jokes, she says, the feel-good factor is more likely to be triggered not by the gag itself, but from the reaction to it.

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

The Search for the Perfect Cracker Joke

Will we ever discover the ultimate gag?

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

In 2001, a psychologist set up a research search for the planet's funniest gag.

More than 40,000 gags later, with ratings provided by hundreds of thousands of people globally, he has a clearer understanding than many as to what works and what does not.

The perfect Christmas cracker joke must be short, he says.

"They must also be poor gags, puns that make us groan," he adds.

The increasingly "awful" the joke, he says the more effective.

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

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

"That's a common experience at the gathering and I believe it's wonderful."