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

This one-liner is greeted with moans that resonate through a storage facility in the capital.

We're at a humor-evaluation meeting with a company that makes supplies for social events. Its catalogue features Christmas crackers.

The firm's founder grins, almost apologetically at the joke. But the pun has been selected and will appear in upcoming crackers.

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

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

"The goal is for the gag to be a thing that brings the eight-year-old in harmony with the grandparent," she states.

The Neuroscience Of Shared Amusement

Coming together to experience shared laughter is not only nothing new, experts say, it is likely to be pre-human.

"Therefore when you are laughing with people at the Christmas table you are dropping into what's very likely a really primordial mammalian social vocalisation," explains a neuroscience expert.

Communal amusement, she explains, aids in forge and strengthen social bonds between people.

Scientists have found that a absence of these interactions can significantly damage mental and physical health.

"The people you talk to, and laugh with, it leads to increased amounts of 'happy chemical' uptake," she continues.

These natural chemicals are the brain's "feel-good compounds" and are released both to alleviate tension and discomfort and in reaction to enjoyable activities, such as laughing with friends over a particularly awful festive cracker gag.

"It's not simply laughing at a foolish pun with a holiday cracker," the expert says. "You are in fact performing a lot of the really vital work of building, preserving the connections you have with the people you love."

What Occurs Inside the Brain?

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

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

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

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

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

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

Put all of this as a whole, and people listening to a pun have a complex series of brain reactions that underpin the amusement we experience.

The Infectious Nature of Chuckles

Researchers discovered that when a humorous word is paired with laughter there is a greater response in the mind than the identical word when accompanied by a non-emotional sound.

"This activation occurred in parts of the mind that you would employ to contort your face into a grin or a laugh," she explains.

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

Laughter, according to the expert, can be infectious.

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

"People laugh harder when you know others," she says, "and laughter increases further when you are fond of them or care for them."

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

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

The Quest for the Ideal Cracker Joke

Will we ever discover the perfect joke?

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

Years ago, a psychologist established a research search for the world's most humorous joke.

Over tens of thousands of jokes submitted, with scores provided by hundreds of thousands of participants around the world, he has a clearer understanding than most as to what succeeds and what fails.

The perfect festive cracker pun needs to be short, he says.

"But they also be bad gags, puns that cause us to groan," he adds.

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

"The reason is that if nobody 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 experience around the gathering and I believe it's wonderful."