Home Alone fans spot major mistake suggesting Kevin wasn’t the only child left behind

This year marks the 35th anniversary of the Christmas classic

Even though you might think you could quote your favourite festive movies word by word, sharp-eyed fans have spotted a hidden detail in perhaps everyone's favourite Christmas film that they had never noticed before.

This year marks the 35th anniversary of the Christmas classic Home Alone.

This tale of a child neglected by parents more obsessed with first-class travel than actually counting their kids hides a major mistake, hinting that eight-year-old Kevin McCallister might not have been the only child left behind.

If you’ve somehow been living under a rock, Home Alone kicks off in the McCallisters’ chaotic Chicago home as the family prepares for their trip to Paris. After a fight with his siblings, eight-year-old Kevin is sent to bed early.

The next morning, Kevin oversleeps. His distracted parents, Kate and Peter, rush to catch their flight, completely unaware that Kevin is missing. He is not on the bus, not at the airport, and not on the plane.

Left alone at home in Chicago, Kevin faces a new problem. When two burglars try to break in, he takes matters into his own hands to protect the family’s valuables.

Now, some of the film’s superfans have noticed that Kevin could never have actually boarded the flight, all because of a subtle detail revealed at the very start of the movie.

During an argument with his brother Buzz over a pizza, a drink ends up spilt on the kitchen counter. Amid the cleanup, a glance reveals Kevin’s plane ticket lying in the bin.

This could explain why they didn't notice that they had one too many tickets. However, another hidden detail in the film implies that another McCallister child has been left behind.

When cousin Heather is doing a headcount for the children getting off the bus, Buzz starts shouting random numbers to throw her off. This causes her to count herself twice, marking herself for both number three and number 11.

When Kate asks if everyone has been counted, Heather replies proudly: "11, including me. Five boys, six girls, four parents, two drivers, and a partridge in a pear tree."

Yet this implies that, with Heather counting herself twice and 11 being the total number of kids, another member of the family must have been left behind somewhere.