Mark Zuckerberg began testing a horizontal swiping feature on Wednesday for his pet project, Threads, the app whose main purpose seems to be trolling Elon Musk. The feature appears to be something Musk tweeted about two weeks ago, noting that he’s wanted to add it to X for the last year.

“Swipe right to reply, left to favorite, tap & hold for all other actions. Very clean,” said Musk in a tweet from Mar. 7. “I’ve been dying to do this for a year.”

Zuck posted on Threads Wednesday about his new feature that’s being tested.

“New thing we’re testing out: swipe to like or tell us you’re not interested in the post,” the Meta CEO posted. “It’s an easy way to let us know what you want to see more of on your feed.”

Let’s not forget, Zuckerberg launched a bare-bones version of Threads less than a year ago to offer an alternative to Musk’s “dying” Twitter. The boyish billionaires jabbed back and forth at each other for days after the initial release.

“Zuck is a cuck,” tweeted Musk shortly after Threads went live.

“Concerning,” said Zuck on Threads, mocking one of Musk’s typical replies.

However, Meta and X’s plans for horizontal swiping vary greatly. Zuck’s idea for left and right swiping is a lot like Tinder; a swipe right will show you similar content, whereas a swipe left will show you less of it. Musk, on the other hand, wants horizontal swiping to replace the like and reply buttons that appear at the bottom of tweets altogether.

Many have speculated that Threads really only needs to be slightly successful to kill off X altogether. Last we heard from the Zuck, Threads had 130 million monthly active users. That’s nothing close to Instagram, but it’s over a hundred million users that won’t be on X.

The feature Threads is testing is notable because it would allow users more control over their algorithm. Instagram and Facebook offer you very little control, but apps like TikTok offer this kind of algorithm toggling. Musk on the other hand seems like he just wants to make his app look cleaner.

Threads is so close to being a good X competitor, but Zuck has made it boring by design. Head of Instagram Adam Mosseri has repeatedly said Threads will not promote news or politics, the same content that drove Twitter to success all these years, deeming it “too risky.” So users must choose between X, where hate speech and misinformation run rampant, or Threads, where there’s not much to get excited about.

Zuck doesn’t announce every new feature on Threads, but when he does, you know he’s shouting it out to one person in particular: Elon Musk. Threads is essentially Zuck’s playground to mess with the owner of X. Given the fact that Musk has been dying to implement horizontal swiping, I’d say it’s working.