"How much did Father Christmas's sleigh cost? Nothing, it was on the house."
This joke is met by moans that echo through a storage facility in the capital.
We're at a joke-testing meeting with a company that makes products for gatherings. Its repertoire features Christmas crackers.
The firm's founder grins, nearly apologetically at the joke. But the joke has been selected and will appear in future crackers.
"You measure the gag by the volume of moans and the loudness of the groans around the table," she says.
The key to a good Christmas cracker pun is not the identical as a stand-up gag per se. It is entirely about the context - in this instance, the communal laughter of the holiday dinner table with grandparents, kids and potentially friends.
"You want the joke to be something that unites the eight-year-old together with the 80-year-old," she states.
Coming together to experience communal amusement is not only ancient, experts say, it is likely to be older than humanity.
"Therefore when you are laughing with people around the Christmas dinner you are engaging in what's almost certainly a really ancient mammalian play vocalisation," says a professor.
Communal laughter, she explains, aids in make and maintain social bonds between individuals.
Scientists have discovered that a absence of these social exchanges can seriously damage both psychological and bodily health.
"Those you talk to, and laugh with, it results in enhanced amounts of 'happy chemical' uptake," she continues.
These natural chemicals are the body's "feel-good compounds" and are released both to alleviate stress and pain and in response to enjoyable experiences, such as laughing with loved ones over a particularly awful Christmas cracker joke.
"It's not simply laughing at a foolish pun with a holiday cracker," she says. "You are in fact performing a lot of the truly important task of building, preserving the connections you have with those you love."
But what is truly taking place inside the mind when we listen to a joke?
A tremendous amount happens in reaction to humour, it transpires.
Using functional magnetic resonance imaging (fMRI), a type of brain scanner which indicates which parts of the mind are more active, researchers have been able to chart the regions that get more blood.
The research entails imaging the minds of volunteer subjects and then subjecting them to a collection of humorous phrases, paired with either a neutral sound, or pre-recorded chuckles.
"During the study we got a very fascinating activation pattern of neural activity," says the professor.
A gag activates not just the parts of the mind in charge of hearing and interpreting speech, but also brain regions involved in both planning and initiating motion and those involved in vision and recall.
Combine these elements together, and individuals hearing a joke have a sophisticated set of brain responses that support the laughter we experience.
Scientists found that when a humorous word is paired with chuckles there is a stronger response in the brain than the same phrase when followed by a neutral sound.
"This activation occurred in parts of the mind that you would employ to move your face into a smile or a chuckle," she explains.
It means people are not just reacting to funny words, they are responding to the amusement that accompanies them.
Laughter, says the professor, can be contagious.
So what does this mean for the chuckles heard around a Christmas table?
"People laugh harder when you know others," she says, "and laughter increases further when you like them or love them."
When it comes to Christmas cracker jokes, she says, the positive effect is more likely to be triggered not by the gag itself, but from the response to it.
"The laughter is key. The joke is the dreadful Christmas cracker joke, and it's just a pretext to chuckle as a group."
Is it possible to discover the perfect gag?
Probably not, but that has not stopped experts from trying to.
In 2001, a psychologist set up a research search for the planet's most humorous gag.
More than tens of thousands of jokes submitted, with scores provided by hundreds of thousands of people globally, he has a clearer idea than most as to what succeeds and what does not.
The perfect festive cracker pun needs to be short, he explains.
"They must also need to be poor gags, jokes that cause us to groan," he adds.
The more "awful" the joke, he says the better.
"This is because if no-one laughs – it's the gag's shortcoming, not yours.
"What's interesting about the holiday cracker jokes is that none of us considers them humorous.
"That's a common experience at the gathering and I think it's lovely."
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