Interstellar fans warned about major plot giveaway you'll only notice watching a second time

If you've watched Interstellar you'll probably agree it's up there as one of the best sci-fi movies of all time.

The heart-wrenching film follows ex-NASA pilot Joseph Cooper (played by Matthew McConaughey) as he sets out with a team of researchers to find a new planet after Earth becomes inhabitable.

The movie was released in 2014. (Paramount Pictures)

But it's not your everyday dystopian sci-fi flick. In fact, it's filled with mind-boggling twists that we come to expect with Christopher Nolan films.

And don't even get us started on how many tears were shed while watching.

Fans will remember that when Cooper and the team travel to space, it becomes clear that the only way to save humanity is to gather data from inside the black hole.

Cooper sacrifices himself and leaves the rest of the team to descend into the black hole in his own spacecraft.

It is here that the 'Tesseract' allows Cooper to essentially travel back in time to provide his daughter, Murphy, clues about the black hole and how humanity can be saved.

Remember Murphy thinking she had a ghost? Well, that was Cooper all along.

The pair end up reuniting at the end of the movie, with Murphy being an elderly woman at this point, while Cooper has barely aged.

It's certainly the kind of film you need to watch a few times to fully pick up on every clever little detail that Nolan included.

In fact, there was one detail that many fans missed when watching it for the first time - the ticking noise when the characters are on the watery Miller's planet.

And if you listen carefully, it actually gives away the entire plot.

When the team arrive, you might have noticed that there's a ticking sound that occurs every 1.25 seconds.

One viewer worked out that considering every hour there is equivalent to seven years on Earth, each tick represents one day.

Turns out the time difference between Cooper and his daughter was right there in front of us all along.

Did you notice the ticking? (Paramount Pictures)

People were pretty blown away when they made the discovery.

One wrote on X: "Did you know that in Interstellar, you can hear a ticking sound every 1.25 seconds in Miller's Planet scene? Now the interesting fact is each tick represents a day passing on earth."

While another said: "The genius Interstellar music on Miller's planet where each background ticking stood for a entire day passing on Earth. The weight of it all, so palpable."

And a third added: "Interstellar was brilliant... I only realised the other day about the ticking sound."

This tiny detail makes the whole scene way more emotional.