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

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

We're at a humor-evaluation session with a company that produces products for social events. Its repertoire includes Christmas crackers.

The firm's founder grins, nearly sheepishly at the gag. But the pun has made the cut and will appear in upcoming crackers.

"The success is gauged by the joke by the volume of groans and the intensity of the groans around the table," she explains.

The secret to a great Christmas cracker joke is not the same as a good gag per se. It is entirely about the setting - in this case, the shared amusement of the Christmas dinner table with grandparents, children 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 adds.

The Neuroscience Behind Communal Laughter

Coming together to enjoy communal laughter is not only nothing new, experts argue, it is probably to be pre-human.

"Therefore when you are chuckling with people around the holiday table you are engaging in what's very likely a truly ancient mammalian play vocalisation," explains a neuroscience expert.

Communal laughter, she says, aids in make and maintain social connections between people.

Scientists have found that a lack of such interactions can significantly harm mental and physical well-being.

"The people you converse with, and share laughter with, it leads to increased amounts of 'happy chemical' release," the professor adds.

Endorphins are the body's "feel-good compounds" and are released both to reduce tension and discomfort and in response to enjoyable experiences, such as laughing with friends over a truly awful Christmas cracker joke.

"It's not simply laughing at a silly pun with a Christmas cracker," the expert states. "You are actually performing a lot of the really vital work of building, preserving the social bonds you have with the people you love."

Which Happens Inside the Mind?

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

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

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

The research involves scanning the minds of volunteer subjects and then subjecting them to a database of funny phrases, accompanied by either a non-emotional sound, or pre-recorded chuckles.

"During the study we observed a very fascinating pattern of neural activity," notes the professor.

A joke activates not just the parts of the mind in charge of auditory processing and understanding speech, but also brain areas associated with both planning and starting movement and those linked to sight and memory.

Put these elements as a whole, and individuals hearing a joke have a complex set of neural responses that underpin the amusement we experience.

The Infectious Nature of Laughter

Researchers discovered that when a humorous phrase is paired with chuckles there is a greater response in the mind than the identical phrase when followed by a non-emotional sound.

"This was in parts of the brain that you would use to move your expression into a grin or a chuckle," she explains.

It means people are not just reacting to funny words, they are reacting to the amusement that accompanies them.

Laughter, says the professor, can be infectious.

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

"People laugh harder when you know people," she says, "and you laugh more when you are fond of them or care for them."

When it comes to Christmas cracker jokes, she says, the positive factor is more probable to be caused not by the gag in itself, but from the reaction to it.

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

The Search for the Ideal Festive Pun

Is it possible to find the perfect joke?

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

Years ago, a psychologist established a scientific search for the planet's most humorous joke.

Over 40,000 jokes submitted, with scores provided by 350,000 people globally, he has a better understanding than many as to what succeeds and what fails.

The ideal Christmas cracker joke must be brief, he says.

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

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

"The reason is that if nobody laughs – it's the joke's shortcoming, not yours.

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

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