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

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

We're at a humor-evaluation meeting with a company that makes supplies for gatherings. Its catalogue features festive crackers.

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

"You measure the gag by the number of moans and the intensity of the groans around the table," the founder explains.

The key to a good Christmas cracker joke is not the same as a stand-up gag in itself. It is entirely about the setting - in this instance, the shared laughter of the holiday meal with elders, kids and potentially neighbours.

"You want the gag to be a thing that brings the eight-year-old in harmony with the 80-year-old," she adds.

The Neuroscience Behind Shared Laughter

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

"Therefore when you are laughing with people around the holiday table you are dropping into what's very likely a truly primordial mammalian play vocalisation," says a neuroscience expert.

Shared laughter, she explains, aids in make and maintain social connections between people.

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

"The people you talk to, and laugh with, it results in enhanced levels of 'happy chemical' uptake," she adds.

Endorphins are the body's "feel-good compounds" and are produced both to alleviate stress and pain and in response to enjoyable activities, such as laughing with loved ones over a truly terrible Christmas cracker joke.

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

What Occurs In the Brain?

But what is actually happening inside the brain when we hear a gag?

A tremendous amount occurs in reaction to comedy, it transpires.

Using functional magnetic resonance imaging (fMRI), a type of brain scanner which indicates which areas of the mind are working harder, researchers have been able to map the regions that receive more blood.

The research entails scanning the brains of volunteer participants and then exposing them to a database of funny words, accompanied by either a non-emotional sound, or recorded chuckles.

"During the study we got a very fascinating pattern of activation," says the neuroscientist.

A joke activates not just the parts of the mind in charge of auditory processing and interpreting language, but also neural areas associated with both preparation and starting movement and those linked to vision and memory.

Combine all of this together, and people listening to a pun have a sophisticated set of neural responses that underpin the amusement we experience.

The Contagious Power of Chuckles

Researchers discovered that when a funny phrase is combined with chuckles there is a greater reaction in the brain than the same word when accompanied by a neutral sound.

"This was in parts of the mind that you would employ to move your face into a grin or a laugh," she explains.

It means we are not just reacting to humorous jokes, they are reacting to the amusement that follows them.

Amusement, according to the expert, can be infectious.

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

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

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

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

The Quest for the Perfect Cracker Joke

Is it possible to discover the ultimate gag?

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

In 2001, a psychologist established a scientific project for the world's funniest gag.

Over tens of thousands of jokes submitted, with ratings lodged by hundreds of thousands of participants globally, he has a better understanding than many as to what succeeds and what fails.

The ideal Christmas cracker pun needs to be short, he says.

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

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

"The reason is that if no-one laughs – it's the gag's shortcoming, not yours.

"The fascinating part about the holiday cracker jokes is that not one person considers them humorous.

"It creates a shared experience at the table and I believe it's lovely."