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

This quip is met by moans that resonate through a storage facility in the capital.

We're at a joke-testing session with a company that makes products for social events. Its catalogue features Christmas crackers.

The firm's owner smiles, almost apologetically at the joke. But the joke has made the cut and will feature in future crackers.

"You measure the joke by the number of groans and the intensity of the groans around the table," she says.

The key to a good holiday cracker pun is not the same as a stand-up gag in itself. It is all about the context - in this case, the communal laughter of the holiday dinner table with elders, kids and possibly neighbours.

"You want the gag to be something that brings the child in harmony with the grandparent," she states.

The Science Of Shared Amusement

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

"Therefore when you are chuckling with people around the holiday dinner you are dropping into what's very likely a really primordial mammalian social sound," says a professor.

Shared amusement, she explains, helps make and maintain social bonds between people.

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

"Those you converse with, and laugh with, it results in enhanced levels of 'happy chemical' release," the professor adds.

Endorphins are the body's "happy chemicals" and are produced both to alleviate tension and discomfort and in reaction to enjoyable activities, such as laughing with friends over a particularly awful Christmas cracker joke.

"It's not simply laughing at a silly joke with a Christmas cracker," she states. "You are actually doing a lot of the truly vital work of building, preserving the connections you have with the people you love."

What Happens Inside the Mind?

But what is truly happening inside the brain when we listen to a joke?

An awful lot occurs in reaction to humour, it turns out.

Employing brain scanning technology, a type of neural imager which indicates which areas of the brain are working harder, researchers have been able to chart the areas that receive more blood.

The research involves scanning the brains of healthy subjects and then subjecting them to a collection of funny phrases, paired with either a neutral sound, or recorded chuckles.

"In the scanner we observed a very fascinating activation pattern of activation," says the neuroscientist.

A joke activates not just the areas of the mind responsible for hearing and understanding speech, but also brain areas involved in both planning and starting motion and those involved in vision and memory.

Put all of this together, and individuals hearing a joke have a sophisticated series of neural responses that support the laughter we hear.

The Contagious Power of Laughter

Researchers discovered that when a humorous phrase is paired with chuckles there is a stronger response in the brain than the same word when accompanied by a non-emotional sound.

"This activation occurred in areas of the mind that you would employ to contort your expression into a smile or a laugh," she explains.

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

Laughter, according to the professor, can be contagious.

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

"People laugh more when you are familiar with others," she notes, "and you laugh further when you are fond of them or care for them."

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

"It's the laughter. The joke is the terrible holiday cracker pun, and it's just a pretext to laugh together."

The Quest for the Perfect Cracker Joke

Is it possible to discover the perfect joke?

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

In 2001, a professor established a scientific project for the world's most humorous gag.

Over tens of thousands of jokes submitted, with ratings lodged by hundreds of thousands of people globally, he has a better idea than many as to what succeeds and what does not.

The ideal festive cracker joke must be short, he says.

"They must also be bad jokes, jokes that make us groan," he continues.

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

"This is because if nobody finds it funny – it's the gag's fault, not your own.

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

"That's a shared experience at the table and I believe it's wonderful."