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

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

We're at a humor-evaluation meeting with a firm that produces products for social events. Its catalogue includes festive crackers.

The firm's owner smiles, nearly apologetically at the gag. But the joke has been selected and will appear in future crackers.

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

The secret to a great holiday cracker pun is not the identical as a stand-up joke per se. It is entirely about the context - in this case, the shared amusement of the holiday meal with elders, children and potentially friends.

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

The Neuroscience Behind Shared Laughter

Gathering to enjoy shared amusement is not only nothing new, experts say, it is likely to be pre-human.

"So when you are laughing with others at the Christmas dinner you are dropping into what's almost certainly a truly primordial mammalian play sound," explains a professor.

Communal laughter, she says, helps forge and strengthen social bonds between people.

Scientists have found that a absence of these social exchanges can seriously harm both psychological and bodily well-being.

"Those you talk to, and laugh with, it results in enhanced amounts of 'happy chemical' uptake," she adds.

These natural chemicals are the brain's "feel-good compounds" and are released both to reduce stress and pain and in response to pleasurable activities, such as laughing with friends over a truly awful festive cracker joke.

"You're not just chuckling at a foolish joke with a holiday cracker," she states. "You are in fact performing a lot of the truly important task of building, preserving the social bonds you have with the people you care about."

What Occurs In the Brain?

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

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

Employing functional magnetic resonance imaging (fMRI), a type of brain scanner which shows which parts of the brain are more active, researchers have been able to map the regions that get more blood flow.

Testing involves imaging the brains of volunteer participants and then subjecting them to a database of humorous phrases, accompanied by either a neutral sound, or pre-recorded laughter.

"In the scanner we got a very fascinating pattern of neural activity," says the neuroscientist.

A joke activates not just the areas of the mind responsible for auditory processing and understanding speech, but also brain regions associated with both planning and initiating movement and those involved in vision and memory.

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

The Contagious Nature of Laughter

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

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

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

Amusement, according to the expert, can be infectious.

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

"You laugh harder when you know others," she notes, "and you laugh further when you are fond of them or love them."

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

"It's the laughter. The gag is the terrible Christmas cracker joke, and it's just a reason to chuckle as a group."

The Search for the Ideal Festive Pun

Will we ever find the perfect gag?

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

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

More than tens of thousands of gags later, with ratings lodged by hundreds of thousands of participants globally, he has a clearer understanding than most as to what succeeds and what does not.

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

"But they also need to be bad gags, puns that make us moan," he continues.

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

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

"The fascinating part about the Christmas cracker puns is that not one person considers them humorous.

"It creates a shared experience around the gathering and I think it's lovely."