'Say cheese' has long become an almost universal command from photographers when you're posing for a photograph.
It's a custom that has passed from generation to generation, and country to country.
But why exactly do we talk about a dairy product when we're posing for a photo?
Dr Graham Finlay - from UCD's School of Politics and International Relations - spoke to Moncrieff about the familiar but unusual expression.
He said: "It started in the western world - in fact, it started quite recently.
"The earliest reference we can find to people saying 'cheese' as a trick to make you give what looks like a smile in a photograph is from the 1940s.
"An ambassador of [US President] Franklin Roosevelt said 'this is a great trick I learned from a prominent politician about how to smile in photographs'. Everyone thought he was talking about the president, and it caught on.
"It started as far as we can tell in the United States, possibly with FDR... and spread around the world really, really quickly."
Decades later, the trick has very much stuck around.
A cheesy grin
What's so effective about the word 'cheese' in particular?
Dr Finlay said: "The 'e' especially really bears your teeth, and gives your mouth the shape of a fake smile - this is not a real smile, and there's a big difference between them.
"All around the world, you actually see people saying different things - but you have to get that 'e' sound. In places like India and Turkey, where paneer is the word for cheese... you get that 'e' sound.
"In Latin American countries, it's more like 'whiskey', where you kind of hold the 'e' at the end of whiskey."
However, he noted that in Japan and Italy people simply use the English word cheese to get the effect.
Dr Finlay said there's also the idea of a 'cheesy grin' - a fake expression.
He observed: "There's a big difference between fake smiles and real smiles - principally around the eyes. If you're saying cheese, your eyes are not going to crinkle and compress the way they do with a genuine smile.
"There's a zillion photographers online recommending ways to get a real smile online... one way is to say '1, 2, 3... say cheese'. You take the picture when people say cheese, and then you fire off the pictures you want to get just after that, when people are relaxed and maybe acting in a more normal way."
Watch the birdie
Dr Finlay also went into the history of another photography-related phase that many children may have been told when posing for a photo: 'watch the birdie'.
He explained: "Around the end of the 19th century, a photographer had an actual bird which he'd use to get people to compose their face or look at him behind his tripod... just to focus your gaze in the right place.
"A bunch of people patented and brought out all these mechanical birds, which allowed photographers to squeeze a bulb - and the bird would sing or move, or otherwise get the attention of children especially.
"This sort of died out as people lost the tripod and hood over the back, as cameras got smaller and shutter speeds got much shorter... so you could really take a snapshot."
You can listen to the full podcast below:
