We are not going to spoil the post-credits scene of Avengers: Infinity War, because waiting for the scene itself is stressful enough. However, if you’re of a certain age, and say, perhaps missed one very brief tech fad in the Nineties, there’s one specific thing about the post-credits scene that might not make sense. In short, the only spoiler here is that someone uses a pager in the Infinity War post-credits scene, but, if you don’t know what a pager is exactly, we’re here to help.

There are no specific spoilers here for the post-credits scene in Infinity War. However, someone does use a pager, and the following article is here to help those who might not know what a pager is exactly.

A character in the final moments of the post-credits scene in Avengers: Infinity War uses a pager. We’re not going to tell you who they are paging because that would be a giant spoiler. But, if you were in high school after the Nineties, you might be like, What the hell is a pager? Sometimes called a “beeper,” a pager was mobile communication technology that predated cell phones.

Here’s how pagers work. When a person wanted to get ahold of someone else, they could use a landline to dial the number of that person’s pager. The pager’s little screen would light up with the number of the person who just “paged” you. Back then, you generally knew everyone’s phone numbers by heart, so you’d instantly know who was trying to call you. The paged person would then go to a landline and dial the number to return the call.

The exact numerals contained in the page could be manipulated by the sender, and sometimes, very simple 8-bit graphics could also be transmitted, but those were often expensive.

All in all, pagers were often popular among criminals like drug dealers because they were harder to track down. For this specific reason, you can imagine why a superhero with an old-school secret identity might want one, too.

Avengers: Infinity War is out everywhere on April 27