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"What was the price did Santa's sled cost? Nothing, it was on the house."

This quip is met by groans that echo through a warehouse in the capital.

We're at a joke-testing meeting with a company that makes supplies for social events. Its repertoire features Christmas crackers.

The company's owner smiles, nearly sheepishly at the joke. But the joke has been selected and will feature in future crackers.

"The success is gauged by the gag by the number of moans and the loudness of the groans at the table," she explains.

The secret to a great Christmas cracker joke is not the same as a good joke in itself. It is entirely about the setting - in this instance, the communal laughter of the Christmas dinner table with grandparents, kids and possibly friends.

"The goal is for the gag to be a thing that unites the eight-year-old together with the grandparent," she adds.

The Science Of Communal Laughter

Coming together to enjoy communal laughter is not only nothing new, scientists say, it is likely to be pre-human.

"So when you are laughing with others around the Christmas dinner you are engaging in what's very likely a truly ancient mammalian social vocalisation," explains a professor.

Communal laughter, she says, helps make and maintain social bonds between individuals.

Researchers have discovered that a absence of such interactions can significantly harm mental and physical well-being.

"Those you converse with, and laugh with, it leads to enhanced levels of 'happy chemical' uptake," she adds.

Endorphins are the body's "happy chemicals" and are produced both to reduce stress and pain and in reaction to enjoyable activities, such as chuckling with friends over a particularly terrible Christmas cracker gag.

"You're not just chuckling at a silly pun with a Christmas cracker," the expert states. "You are in fact doing a lot of the really vital work of building, preserving the social bonds you have with the people you love."

Which Occurs In the Brain?

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

An awful lot occurs in reaction to comedy, it transpires.

Employing brain scanning technology, a type of neural imager which shows which areas of the mind are working harder, scientists have been able to map the regions that get more blood flow.

The research involves scanning the minds of volunteer participants and then exposing them to a collection of humorous words, accompanied by either a neutral sound, or pre-recorded laughter.

"In the scanner we observed a really fascinating activation pattern of activation," notes the professor.

A joke stimulates not just the areas of the brain in charge of auditory processing and understanding speech, but also brain regions associated with both planning and starting movement and those linked to vision and recall.

Combine all of this together, and people listening to a joke have a sophisticated set of neural reactions that support the amusement we hear.

The Contagious Nature of Chuckles

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

"This was in parts of the brain that you would use to contort your face into a grin or a laugh," she explains.

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

Amusement, according to the expert, can be infectious.

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

"People laugh harder when you are familiar with people," she notes, "and laughter increases more when you like them or love them."

When it comes to Christmas cracker jokes, she explains, the feel-good effect is more probable to be caused not by the joke in itself, but from the response to it.

"It's the laughter. The gag is the dreadful holiday cracker pun, and it's just a pretext to laugh as a group."

The Search for the Perfect Cracker Joke

Will we ever find the ultimate joke?

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

Years ago, a professor set up a research search for the planet's funniest joke.

More than tens of thousands of jokes later, with scores provided by hundreds of thousands of people globally, he has a better idea than many as to what succeeds and what does not.

The perfect Christmas cracker joke needs to be short, he explains.

"But they also be poor jokes, puns that cause us to moan," he continues.

The increasingly "terrible" the joke, he states the better.

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

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

"It creates a common experience at the table and I think it's wonderful."