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

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

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

The firm's founder smiles, almost apologetically at the gag. But the pun has made the cut and will feature in upcoming crackers.

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

The key to a good Christmas cracker pun is not the same as a stand-up joke in itself. It is all about the setting - in this case, the shared laughter of the holiday meal with grandparents, children and possibly friends.

"You want the gag to be something that unites the eight-year-old together with the grandparent," she adds.

The Neuroscience Of Communal Amusement

Gathering to enjoy shared laughter is not only ancient, scientists say, it is likely to be older than humanity.

"Therefore when you are laughing with others at the holiday dinner you are dropping into what's almost certainly a truly primordial mammalian play sound," explains a neuroscience expert.

Shared laughter, she explains, helps make and maintain social bonds between individuals.

Researchers have discovered that a lack of these social exchanges can significantly damage mental and physical well-being.

"Those you converse with, and share laughter with, it results in increased amounts of 'happy chemical' uptake," the professor continues.

These natural chemicals are the body's "happy chemicals" and are produced both to reduce stress and pain and in reaction to pleasurable activities, such as laughing with friends over a particularly awful Christmas cracker gag.

"It's not simply laughing at a silly joke with a Christmas cracker," she states. "You are actually doing a lot of the really important task of making, maintaining the connections you have with the people you care about."

What Occurs In the Brain?

But what is truly taking place within the mind when we listen to a gag?

An awful lot happens in reaction to comedy, it turns out.

Using functional magnetic resonance imaging (fMRI), a type of neural imager which indicates which parts of the brain are more active, scientists have been able to map the areas that receive more blood flow.

Testing entails scanning the minds of healthy participants and then exposing 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 interesting activation pattern of activation," says the professor.

A joke activates not just the areas of the brain in charge of hearing and interpreting language, but also neural regions involved in both planning and starting movement and those involved in vision and recall.

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

The Contagious Power of Laughter

Scientists found that when a humorous word is paired with chuckles there is a stronger response in the mind than the same word when accompanied by a non-emotional sound.

"This activation occurred in parts of the brain that you would use to contort your expression into a smile or a chuckle," she explains.

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

Laughter, says the professor, can be infectious.

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

"People laugh more when you are familiar with others," she says, "and you laugh further when you like them or care for them."

When it comes to festive cracker jokes, she says, the positive effect is more probable to be triggered not by the joke in itself, but from the response to it.

"The laughter is key. The joke is the dreadful Christmas cracker pun, and it's just a pretext to chuckle as a group."

The Search for the Perfect Festive Pun

Is it possible to find the ultimate joke?

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

Years ago, a psychologist established a scientific project for the world's funniest joke.

Over 40,000 gags later, with scores provided by hundreds of thousands of participants around the world, he has a better idea than most as to what succeeds and what does not.

The ideal festive cracker pun must be brief, he explains.

"They must also need to be bad gags, jokes that cause us to moan," he continues.

The more "terrible" the gag, he states the better.

"This is because if nobody finds it funny – it's the gag's shortcoming, not yours.

"What's interesting about the holiday cracker puns is that none of us find them humorous.

"It creates a shared moment around the table and I believe it's wonderful."