Facebook is putting a long-hidden feature back in the spotlight.

The Poke feature, which was part of Facebook at its start, has seen a 13-fold increase in use in the past month, the company announced in a Thread this week. That comes after Facebook made the feature easier to find after essentially burying it in the bowels of the social media app for years.

Facebook is also once again suggesting who to poke.

Despite the impression that the poke had gone away years ago, it was always available. Facebook just downplayed the feature for years as it experienced massive growth and began expanding its business into a variety of fields, most recently artificial intelligence.

But everyone loves a walk down memory lane—even Mark Zuckerberg. Ironically, it’s not the people who remember this feature who are using it most. More than 50% of the pokes are coming from younger users between the ages of 18 and 29.

What is a poke? Honestly, no one knows. And that’s hardly a new phenomenon. Even the initial users of Facebook were flummoxed by the feature, but that didn’t stop them from using it.

“Let’s say some girl would add me on Facebook who I hadn’t really met,” Chad Brown, a member of the Harvard class of 2007 told the Harvard Crimson on Facebook’s 10th anniversary. “I’d be talking to my roommates and ask, ‘What do you think about this? What does this mean? Is she interested? I’m not sure what to think?’ So they’d say, ‘Well, send her a poke and see what happens.’ … I like the poke.”

Facebook tried to co-opt the Poke name into a messaging service over a decade ago, but that failed quickly.

The Poke was reportedly the brainchild of Zuckerberg, who has steadfastly refused to explain what it’s about.

“We thought it would be fun to make a feature that has no specific purpose,” said Zuckerberg in a Facebook post from long, long ago. “So mess around with it, because you’re not getting an explanation from us.”

Zuckerberg so enjoyed the poke that the initial notification noise that played when you poked someone was reportedly a voice recording of the founder saying, well, “poke”.