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

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

This describes a humor-evaluation meeting with a company that produces supplies for gatherings. Its repertoire includes Christmas crackers.

The company's founder smiles, almost apologetically at the gag. But the joke has been selected and will feature in future crackers.

"The success is gauged by the joke by the number of groans and the loudness of the groans around the table," the founder says.

The secret to a good Christmas cracker joke is not the same as a good joke in itself. It is all about the context - in this instance, the communal amusement of the holiday meal with grandparents, kids and potentially neighbours.

"The goal is for the gag to be a thing that unites the child together with the grandparent," she states.

The Science Behind Communal Laughter

Gathering to experience shared laughter is not only nothing new, experts argue, it is likely to be pre-human.

"So when you are chuckling with people at the Christmas dinner you are engaging in what's very likely a truly primordial mammal play vocalisation," says a professor.

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

Researchers have found that a absence of such social exchanges can seriously harm both psychological and bodily health.

"The people you talk to, and share laughter with, it leads to enhanced levels of 'happy chemical' release," the professor continues.

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

"You're not just laughing at a silly joke with a Christmas cracker," she states. "You are actually doing a lot of the truly important work of making, maintaining the connections you have with the people you care about."

What Happens In the Mind?

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

A tremendous amount happens in reaction to humour, it transpires.

Using brain scanning technology, a type of brain scanner which indicates which areas of the mind are working harder, researchers have been able to chart the areas that receive more blood flow.

Testing involves imaging the brains of volunteer subjects and then subjecting them to a collection of funny words, paired with either a non-emotional sound, or pre-recorded laughter.

"During the study we observed a really fascinating activation pattern of activation," notes the neuroscientist.

A joke stimulates not just the parts of the mind responsible for hearing and understanding language, but also brain areas involved in both preparation and initiating movement and those involved in sight and memory.

Combine these elements as a whole, and individuals listening to a joke have a sophisticated series of neural responses that support the amusement we experience.

The Contagious Power of Chuckles

Scientists found that when a humorous phrase is combined with chuckles there is a greater reaction in the brain than the same word when followed by a non-emotional sound.

"This activation occurred in parts of the brain that you would employ to move your face into a smile or a laugh," the professor explains.

It indicates people are not just reacting to humorous jokes, they are responding to the laughter that follows them.

Laughter, says the professor, can be infectious.

So what does this mean for the chuckles heard around a holiday table?

"People laugh harder when you know people," she says, "and you laugh further when you are fond of them or love them."

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

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

The Search for the Ideal Cracker Joke

Will we ever discover the perfect joke?

Probably not, but that has not stopped experts from trying to.

Years ago, a professor established a scientific search for the world's most humorous gag.

Over 40,000 jokes later, with ratings lodged by 350,000 people globally, he has a clearer idea than many as to what works and what does not.

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

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

The increasingly "awful" the gag, he states the more effective.

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

"What's interesting about the Christmas cracker puns is that not one person considers them humorous.

"That's a shared moment around the table and I think it's lovely."