"What was the price did Father Christmas's sleigh cost? Zero, it was on the house."
This one-liner is greeted with groans that echo through a warehouse in the capital.
We're at a humor-evaluation meeting with a firm that makes supplies for gatherings. Its catalogue includes festive crackers.
The firm's founder smiles, nearly apologetically at the joke. But the pun has made the cut and will appear in future crackers.
"The success is gauged by the gag by the volume of groans and the intensity of the groans around the table," the founder explains.
The secret to a great Christmas cracker joke is not the same as a stand-up joke per se. It is entirely about the setting - in this case, the shared laughter of the holiday meal with grandparents, children and potentially neighbours.
"The goal is for the joke to be a thing that brings the eight-year-old together with the grandparent," she states.
Coming together to enjoy shared amusement is not only ancient, scientists argue, it is likely to be older than humanity.
"So when you are laughing with people at the Christmas dinner you are dropping into what's very likely a truly primordial mammal play vocalisation," explains a professor.
Shared laughter, she explains, aids in make and maintain social bonds between individuals.
Researchers have found that a absence of these interactions can seriously damage mental and physical health.
"Those you converse with, and share laughter with, it leads to increased amounts of 'happy chemical' release," the professor adds.
These natural chemicals are the brain's "feel-good compounds" and are produced both to alleviate tension and discomfort and in reaction to pleasurable experiences, such as laughing with loved ones over a particularly awful Christmas cracker joke.
"It's not simply laughing at a silly joke with a holiday cracker," the expert says. "You are actually performing a lot of the really vital task of making, maintaining the connections you have with those you care about."
But what is actually happening within the mind when we hear a joke?
A tremendous amount happens in response to comedy, it turns out.
Using functional magnetic resonance imaging (fMRI), a type of neural imager which shows which areas of the mind are working harder, researchers have been able to map the regions that get more blood.
The research involves imaging the minds of healthy participants and then exposing them to a database of humorous words, accompanied by either a non-emotional sound, or recorded chuckles.
"In the scanner we observed a really interesting pattern of neural activity," says the professor.
A gag stimulates not just the areas of the mind in charge of hearing and understanding speech, but also brain regions associated with both planning and starting movement and those involved in vision and recall.
Put all of this together, and people hearing a pun have a complex series of brain reactions that underpin the amusement we hear.
Researchers found that when a humorous word is paired with laughter there is a stronger reaction in the brain than the same phrase when accompanied by a non-emotional sound.
"This was in parts of the mind that you would use to move your expression into a smile or a chuckle," she explains.
It means people are not just reacting to humorous words, they are responding to the laughter that follows them.
Amusement, says the expert, can be infectious.
So what does this mean for the chuckles found at a holiday table?
"You laugh harder when you know others," she says, "and you laugh further when you like them or care for them."
When it comes to Christmas cracker puns, she explains, the feel-good factor is more probable to be caused not by the gag itself, but from the reaction to it.
"It's the laughter. The joke is the terrible Christmas cracker joke, and it's just a reason to chuckle together."
Will we ever discover the perfect gag?
Likely not, but that has not stopped researchers from trying to.
Years ago, a psychologist established a scientific search for the planet's funniest joke.
Over 40,000 jokes later, with ratings provided by 350,000 participants around the world, he has a better idea than most as to what succeeds and what does not.
The ideal Christmas cracker pun must be short, he explains.
"But they also be poor gags, puns that cause us to groan," he continues.
The more "awful" the joke, he states the more effective.
"The reason is that if nobody laughs – it's the joke's shortcoming, not your own.
"What's interesting about the holiday cracker puns is that none of us find them funny.
"That's a shared moment at the gathering and I think it's lovely."
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