Cracker jokes and custard chemistry: ways to smuggle science into Christmas

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Christmas may seem like a time for switching off and suspending disbelief but there are plenty of ways to introduce a little science into the celebrations.

We asked experts for their top home experiments to challenge friends and family.

Sweet science

Matthew Cobb, a professor of zoology at the University of Manchester, suggests picking a sweet such as a jellybean and, with your eyes shut and holding your nose, putting it in your mouth and chewing, keeping your mouth shut.

“See if you can tell what the sweet tastes of – you will probably just say ‘sweet’ and maybe have a vague idea of something else,” says Cobb. “After five seconds, take your fingers off your nose and you should get a sudden rush of sensation that enables you to correctly identify the flavour.”

A more extreme version of this experiment, he says, involves grating an onion and an apple, separately, then tasting each on a spoon with your eyes shut and your nose firmly held. “They should taste the same – until you take your fingers off your nose.”

Cobb says such experiments show how flavour largely consists of smell, not taste. “When we chew, the volatile smells emitted by the food go up into our nose via the back of our mouth, where they stimulate our olfactory neurons,” he says, adding that it is the combination of taste and smell that produces flavour.

“Without smell, things don’t taste of much. We all discovered this during the first outbreak of Covid, when people temporarily lost their sense of smell.”

Have a laugh

With crackers a staple of Christmas, Sophie Scott, a professor of cognitive neuroscience at University College London suggests experimenting to see what can influence whether or not people laugh at a (terrible) joke.

“First, try reading those jokes to yourself and see if you laugh at any of them,” she says. “Second, read the jokes to someone else – maybe a room full of people.”

Scott says to look and see if anyone laughs – including you – when you get to the punchline, or if they respond in some other way such as groaning. She notes that although we associate laughter with jokes and humour, we laugh mainly for social reasons.

“You are 30 times more likely to laugh if there is someone else with you than if you are on your own,” she says. “What this means for cracker jokes is that a joke read by someone alone is much less likely to make them laugh than the same joke read – or heard – in company. And laughter is amplified by social connection, so the more you know and like the people that you are with, the more laughter there will be.”

Get stuck into the festive fowl

If you are having a turkey or another bird for your Christmas meal then take time to explore the carcass.

“We did a Thanksgiving dinner a few weeks ago and I got an enormous turkey, cooked the thing for a few hours, basted it lovingly every 30 minutes or so,” says Steve Brusatte, a professor of palaeontology and evolution at the University of Edinburgh. “Mostly so it would be delicious, but also so the meat would fall off the bone well enough that I could remove the bones and show my wife and my six-year-old boy the shoulder area.”

That allowed Brusatte to demonstrate how the various bones fit together to move the wing up and down, and how the huge springy wishbone stores energy as the wings beat.

“This is a simple thing that you can do with a roast turkey or chicken – actually look at the bones and understand how they fit together and move, and that gives a better understanding of biomechanics and flight motions than I’ve ever seen in any textbook during my many years of study,” he says. “And then you get a delicious meal afterwards.”

Prof Sue Black, a forensic anthropologist, anatomist and academic at the University of Oxford, also recommends dissecting the festive bird to understand the anatomy of motion.

“Boil the carcass so that only the bones are left and you have a 3D jigsaw to reconstruct,” she says.

Chemistry of Christmas

Salt is commonly spread on pavements in the winter and there is a simple experiment that can help to explain why.

“You will need 500ml of full-fat milk or cream, five egg yolks and 125g of sugar. A bit of vanilla never goes amiss,” says Andrea Sella, a professor of inorganic chemistry at UCL.

“Whisk them together and then warm almost to the boil until the mixture starts to thicken. Let it cool to room temperature. Meanwhile, get some ice from the freezer. Either bash it, like an alchemist, with a mortar and pestle, or grind it up in a blender like a modernist.”

Next, he says, take two plastic bags – ideally zippable ones. “Drop some of your crushed ice into one and add generous amount of salt. Into the second, spoon some of your custard mixture, adding sprinkles, nuts or bits of fruit. Seal the [second bag] and put it into the first.

“Now mash the ice and salt together, and the custard in the bag. The temperature will plunge, to -10C or even lower. In seconds you’ll have ice-cream, a soft (and delicious) solid.”

Sella says this happens because the dissolved salt prevents liquid water molecules, produced as the ice melts, from freezing back on to the remaining ice.

“So the ice keeps melting and steals heat from the custard (and your fingers),” he says. “It’s practical magic – also known as science.”

Festive pi(e)

“One of the most surprising little science experiments you can do at home is called Buffon’s Needle, but for festive purposes let’s call it Buffon’s Pine Needles. It’s a way of approximating the value of ϖ,” says Kit Yates, a professor of mathematical biology and public engagement at the University of Bath.

First off, grab a bunch of pine needles and select as many as you can that are roughly the same length (L). “Let’s say you manage to find a total (T) of similar-sized pine needles. You’re going to also need a piece of paper that has lines ruled on it which are a distance W apart – further apart than the length of your needles,” Yates says.

Scatter the pine needles, without aiming, on top of your piece of ruled paper and then count the number of needles that cross one of the lines. This number is C.

Once you have counted, you can find your approximation of ϖ by plugging your numbers into this formula: ϖ ≈ 2LT/CW

“What I love about this is that it demonstrates how ϖ seems to crop up in really unusual places,” Yates says. “It feels almost like magic, but it’s just probability in action on your living room floor.”