As Christmas movies go, Home Alone has a fairly straightforward plot line. Kevin McCallister gets left home alone by his family, antics ensue. 

But there's been one detail in the movie that has always annoyed us a little… and lots of other people too, it would seem.

Early on in the movie, a storm causes trees to fall on phone lines, meaning Kevin can't contact his mum and dad to let them know he's okay.

And yet later in the film, he successfully orders a cheese pizza (and manages to terrify the delivery man in the process).

So, before the days of mobile internet and all that jazz, how on earth did Kevin make a phone call with a broken phoneline?

Well, you'll sleep easy tonight because we've finally solved the mystery… with the help of some logical thought from a Reddit user on a thread about movie plot holes.

"I always assumed the tree actually severed the main trunk line to the whole town, but local calls within the same exchange still worked," the quick-thinking Home Alone fan wrote.

To set the record straight, the Huffington Post contacted American telecommunications company AT&T, who says the theory is definitely a solid one.

"Everything is changing now because of all this phone capability is moving into the cloud, but in 1990, that was absolutely a plausible scenario," spokesperson said.

"When you're trying to call from Paris, now you're relying on a whole series of connections including undersea cables, any one of which could have a problem, which would prevent you from reaching some particular telephone number."

Plot hole or not, that pizza scene is still one of our faves, for this line alone: