The most stunning and important moment of Sunday night’s second presidential debate came when Donald Trump threatened to throw Hillary Clinton in jail. What was Clinton’s alleged crime?

During his debate answer about why he would appoint a special prosecutor to investigate Clinton—and to lock her up—he brought up her email scandal. Specifically, he repeatedly mentioned the notion that Clinton had “acid washed” her emails.

“The thing that you should be apologizing for are the 33,000 e-mails that you deleted and that you acid washed,” he said right before calling for that special prosecutor.

“You delete 33,000 e-mails. And then you acid wash them, or bleach them, as you would say—a very expensive process,” Trump continued, again just before reiterating his call for that prosecutor.

What the hell was he talking about and did he literally mean that he believed Hillary Clinton had poured chemicals on her email servers, or her emails?

We explained the first question before when Trump used the line that Clinton “bleached” her emails earlier in the campaign. As my colleague Josh Voorhees described last month, Trump was apparently referring to news reports that Clinton had used a software tool called BleachBit—which deletes emails through a process that does not involve pouring chemicals on emails or an email server, but is a computer program—to delete the emails that her team considered private and that were stored on the same server as her state department work emails. As Laura Wagner also noted in Slate, Bleachbit is a free, open-source software program and thus using it is not a very expensive or complicated process (and also not very effective for somebody trying to permanently destroy evidence of crimes). Acid washing—a process for making jeans look cool if you are on an episode of Miami Vice—appears to be Trump’s shorthand for either bleaching or using BleachBit.

The second question is a bit more difficult to answer. The site Motherboard seems to think Trump was using a metaphor:

But the simplest answer is that Donald Trump was using a lexicon familiar to him to describe an unfamiliar process. A hotel owner understands the cleaning power of bleach. A Man in his 70s knows exactly what acid washing does to fabric and probably assumes it has the same effect on data. The fact that acid wash is again relevant in 2016 should be a separate and perhaps more alarming cause for concern.

After he repeatedly talked about “bleaching” or “acid washing” emails on the campaign trail, Factcheck.org reached out to his campaign to find out what he might have meant. “His campaign told us Trump didn’t literally mean that Clinton ‘acid washed’ her emails,” the site reported in a story on Sept. 8. “It said that he was using a play on words, referring to Clinton’s joke a year ago about ‘wiping’ her server with a cloth.”

Factcheck’s writers were skeptical, though, noting: “Sorry, we don’t get the play on words, which was not clear in any of Trump’s remarks.”

At least on one occasion, though, Trump definitely literally meant that she had used chemicals to destroy her emails. How do we know? Because he said so.

In an August speech in Everett, Washington, Trump said this:

Thirty three thousand emails that she deleted. They’re gone. And not only deleted folks, she bleached—which somebody said they had never even heard of—in a very expensive fashion, used chemical so nobody will ever be able to see ‘em. Who does this?

Yes. “Used chemical so nobody will ever be able to see ‘em.” Here’s the video of him saying these things:

On Monday, to chants of “lock her up,” Trump repeated his claim about bleaching and seemed to again be describing a literal process of chemical bleach.

“Crooked Hillary’s e-mails were bleached and destroyed—now nobody bleaches them,” he told a crowd in Pennsylvania. “You know what, bleaching was so expensive. It’s really a very expensive process. But when you bleach them, it pretty much means they are gone. Though I heard you can’t get rid of e-mails.”

Here’s my personal theory for what might be going on:

Donald Trump believed at one point that Hillary literally poured chemicals on her email server—or maybe on her emails themselves—in order to destroy them because Donald Trump knows terrifyingly little about computers, may have never used one before, and rarely uses email.

Donald Trump is the sort of man who, if he is corrected by an underling, will either have that underling fired or ignore said underling, especially when the thing being corrected demonstrates his own remarkable ignorance and stupidity. Donald Trump’s underlings are too cowardly to explain to him why he’s wrong here, or have told him and been ignored. Either that, or he was corrected, processed that correction, but liked this description so much as an ambiguous and deceptive attack line that his supporters might take literally that he decided to continue to use it on the trail.

We have reached out to the Trump campaign to ask if Trump still believes that Clinton literally used chemicals to destroy her emails as he stated in August, and will update this post if we get a response.

Read more Slate coverage of the 2016 campaign.