Tesla and SpaceX founder Elon Musk’s $44 billion deal to purchase Twitter has been put on hold following his concern that the social media giant hasn’t been honest about the percentage of accounts that are fake.

In a telling back and forth on the platform with current Twitter CEO Parag Agrawal, Musk said that, according to his own people’s estimates, at least 20% of Twitter accounts are fake users or “spam bots.” Musk said Twitter is grossly undercounting its number of fake accounts.

Indeed, the gulf is a wide one. “Our actual internal estimates for the last four quarters were well under 5%,” Agrawal responded. “The error margins on our estimates give us confidence in our public statements each quarter.” Agrawal then interestingly added: “Unfortunately, we don’t believe this specific estimation can be performed externally, given the critical need to use both public and private information (which we can’t share). Externally, it’s not even possible to know which accounts are counted as mDAUs [monetizable daily active users] on any given day.”

In other words, Agrawal is saying that Musk cannot know the genuine number or percentage of fake accounts without Twitter’s internal data, and evidently he cannot have that data until the sale is complete. Musk, for his part, has drawn a line in the sand. “My offer was based on Twitter’s SEC filings being accurate,” he said. “Twitter’s CEO publicly refused to show proof of <5%. This deal cannot move forward until he does.”

Agrawal obviously dismissed external estimates, but a recent audit by software firm SparkToro found, for example, that 49.3% of Joe Biden’s Twitter followers are fake. (No doubt all of this 81 million votes are real, though!) OK, to be fair, roughly the same was estimated for Donald Trump in 2017, and it’s likely true for any number of popular accounts. That certainly doesn’t support Agrawal’s argument.

So, has Twitter been lying to its investors and the Security and Exchange Commission, or is Musk raising the objection in an effort to renegotiate the price? Since last week, Twitter’s stock value has dropped nearly 10% because investors are clearly worried that Musk may back out.

If Musk were to back out, he’d be on the hook for $1 billion — not a small chunk of change even for him. But if it saved him from seriously overpaying for a social media company that’s possibly one-fifth smaller than advertised, then it would save him a lot of dough.

No matter how one slices it, Musk has Twitter’s board on its heels. It can either see the deal scuttled and face the wrath and maybe lawsuits of shareholders, or it can reveal that Musk is right and undermine the company’s value.

Some are even wondering if Musk’s plan from the beginning was not to acquire Twitter at all but rather to expose it and break it. If anyone budges, it will likely be the Twitter board, as Musk clearly has the upper hand.