Elon Musk, the owner of X — the platform previously known as Twitter — took swipes at competitor Meta, saying Mark Zuckerberg is not active on Twitter rival Threads.

The billionaire offered his opinions of Meta and its platforms during the latest episode of “The Joe Rogan Experience” podcast, which aired on Tuesday. Besides trashing Meta, Musk touched on a wide variety of topics, ranging from Tesla’s Cybertruck to the courtroom sketches of disgraced FTX founder Sam Bankman-Fried.

“Yeah, it’s eerily quiet,” Musk said after host Joe Rogan called Threads a “ghost town” despite its record-breaking launch.

“I mean, Zuck himself doesn’t post,” Musk continued. “You got to use your own product.”

Musk’s criticisms of Zuckerberg are odd, considering that the latter does use Threads quite often.

Zuckerberg — who has 3.5 million followers on the platform so far and usually posts on Threads every one to two weeks — last posted about the platform rolling out polls and GIF attachments five days ago, per Insider’s review of his Threads account. He also interacts with other users on the platform by replying to their posts.

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That is, of course, a far cry from Musk’s activity on his own platform, X. Musk posts multiple times daily and is also a prolific replier to other X users.

During the conversation, Musk also mocked Meta-owned Instagram after Rogan mentioned the platform’s integration with Threads.

“There was a time when I was posting on Instagram, but I found myself doing selfies. And I’m like, ‘What the hell is wrong with me?’ Why am I posting selfies to get likes? This is crazy,” Musk said while laughing.

This isn’t the first time Musk has expressed scorn at Zuckerberg’s attempt to develop a Twitter rival. The mercurial billionaire has gone from challenging Zuckerberg to a cage fight to dunking on Instagram on Threads’ launch day.

Meta introduced Threads in July following rumors that they were developing a Twitter competitor. The text-based app was initially warmly received, with over ten million people signing up within the first seven hours of its launch. And according to data intelligence platform Apptopia, the number of monthly active users on Threads reached 120 million users in October, up from 100 million in July.

While the platform wasn’t able to sustain its early momentum, Zuckerberg has been sanguine about Threads’ growth prospects.

“There’s still a lot of basic functionality to build, and once we feel like we’re in a very good place on that, then I’m highly confident that we’re gonna be able to pour enough gasoline on this to help it grow,” Zuckerberg told analysts during Meta’s second-quarter earnings conference call in July.

Representatives for Musk and Zuckerberg did not immediately respond to requests for comment from Insider sent outside regular business hours.