If you ever wondered what was in the box, you might have already seen it in a later movie.

Movie fans have been left pretty astounded after realising that an important detail from a classic Brad Pitt movie is linked to a film starring Gwyneth Paltrow.

The unusual link begins with the 1995 movie, Se7en, which tells the story of police officer William Somerset (played by Morgan Freeman) and cop David Mills (Brad Pitt).

The unusual link begins with the 1995 movie, Se7en. (New Line Cinema)

The pair are working together to hunt down a serial killer, who eventually turns out to be a man named John Doe (Kevin Spacey).

In a horrific twist, it turns out that Doe kills Tracy (Mills’ wife, played by Paltrow) – as well as their unborn child – because he envied Mills.

Towards the end of the movie, Mills is sent a box that contains Tracy’s severed head.

Apparently, viewers were going to be shown the head, but it was decided that instead of revealing the prop, there would be more mystery created by not showing it at all.

But for those who really wanted to see it, all they really needed to do was watch the movie Contagion, which came out in 2011.

The plot of the movie centres around a highly contagious virus that takes over the planet.

Paltrow plays Beth who dies early on in the movie, but importantly, a scene is included in the movie which sees an autopsy performed on Beth’s body.

In it, her brain is analysed and guess what?

The very same prop originally created for Se7en is used.

TikToker @glittering_ghostwriter spoke about how it all came about.

They said: “We never got to see what was in the box unless a few years later you went on to watch the movie Contagion, because then you actually did see what was in the box.”

Explaining they were personally curious to see the prop that the crew created, the TikToker added: “Since they already had a perfectly good, unused prop of Gwyneth Paltrow’s severed head they just used that for the scene in Contagion.”

People were pretty stunned, with one writing: “That is one of the coolest fun facts ever!!”

While another said: “That’s crazy that they would still have the very same prop head 16 years later kinda hard to believe it wouldn’t have gotten lost or destroyed but ok.”

And a third added: “I didn’t know they’d used THE prop but I remember watching Contagion & thinking that we finally got to see what was in the box!”