We're all well versed with the plot of Home Alone by now and the film title is pretty self explanatory too.
Macaulay Culkin shot to fame after playing mischievous eight-year-old Kevin McCallister in the 1990 festive film, who ends up getting left behind while his family head on a trip to France without him.
We've all wondered how his parents Kate and Peter McCallister (Catherine O'Hara and John Heard) somehow managed to forget about their youngest son and only realised when they're thousands of feet in the air en route to Europe.
On top of being left to fend for himself, poor Kevin had the added responsibility of defending the family home from two bumbling burglars, Harold 'Harry' Lyme (Joe Pesci) and Marvin 'Marv' Merchants (Daniel Stern).
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Childline would have had a field day with this brood.
Many theories about the blonde-haired kid's abandonment have floated about over the years, but there is one particular hypothesis that seems to add up - especially as there is hard evidence to back it up in the actual film.
Diehard Home Alone fans will remember what happened the night before the McCallister's are off to the airport, but if you need a reminder, the full family are sitting down to eat pizza and Kevin's order of plain cheese is no where to be seen.
That's because his brutish brother Buzz has already scoffed the lot - even though he is well aware his younger sibling doesn't enjoy the same toppings as his relatives; sausage, olives and onions to be specific.
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Kevin is obviously pretty gutted he hasn't got any tea and Buzz is on the wind up, telling him if he still wants to eat the cheese pizza 'someone will have to barf it all up'. Lovely.
The eight-year-old sees red and charges at the scran stealer, sending him flying backwards into several cups of milk which spill all over the family's passports and plane tickets.
His dad Peter sees the soggy consequences of the scuffle and bounces up to try and save their soaked travel documents - before dozens of hands join in the mopping up process.
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The camera keeps its focus on the McCallister family patriarch though throughout the scene and hones in on what else he has got scrunched up in one of the napkins that he used to clear up the milk mess.
It's a blink and you'll miss it moment, but some eagle eyed viewers spotted that Peter accidentally tossed one of the American Airline's pamphlets into the trash too - which has Kevin's name written on the top.
The young protagonist is then banished to the attic for the night and he storms upstairs, wishing that he never sees any of his family members again - which obviously then sort of comes true.
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The next day, while the rest of the McCallister's are piling in the minibus and heading off to the airport, a small kid from the neighbourhood is having a whale of a time rifling through their luggage and is accidentally included in the head count.
These two major errors - the binned plane ticket and the botched roll call - help to explain how the family managed to board a plane and fly thousands of miles before realising that the little fella had been left behind.
Social media users have shared their theory online after spotting the tiny detail in the plot and people agreed it was a plausible explanation.
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One said: "I have seen Home Alone probably 1 billion times, but was today years old when I realised they threw out Kevin's plane ticket during the pizza debacle and that's why no one figured out he was gone earlier at, like, the airport."
Another wrote: "Watching Home Alone for the 50th time and I've never noticed that in the starting scene when there is a fight in the kitchen, Kevin's ticket is put in the bin. Who knew?"
Still, at least he made the best of a bad situation by torturing a couple of clumsy burglars.
Featured Image Credit: 20th Century FoxTopics: TV and Film, Christmas, Home Alone, Macaulay Culkin