Tesla CEO Elon Musk has thrown the latest punch in his ongoing fight with Mark Zuckerberg over the future of Artificial Intelligence, describing the Facebook founder’s understanding of the subject as “limited” in a cutting tweet.

Musk made his disparaging comment after Zuckerberg said during a Facebook Live stream on Sunday that people who are fearful of AI are “pretty irresponsible.” Musk, who is famously skeptical about AI, has described it “the greatest risk we face as a civilization” and has called for swift government regulation that same month.

Zuckerberg, who hosted a live, hour-long broadcast while waiting for his dinner to reach the perfect temperature, went on to list ways he believed AI would improve — and is already improving — human lives in different ways. “I have pretty strong opinions on this. I am optimistic.”

But on Tuesday, Musk responded to a tweet which linked to a Biz Journals piece about Zuckerberg criticizing what he described as the Facebook chief’s “pretty irresponsible” warnings against AI. “I’ve talked to Mark about this. His understanding of the subject is limited,” he wrote to his 10.6 million followers.

I've talked to Mark about this. His understanding of the subject is limited.

— Elon Musk (@elonmusk) July 25, 2017

In response to a post by a Twitter user which said Musk should provide “some very strong arguments in a well written blog piece to win over the (myself included) skeptics,” the Tesla and SpaceX CEO wrote: “Movie on the subject coming soon…” Now, why hasn’t anyone thought of that before?