As if the Brexit negotiations aren't tense enough, a "nebulous" linguistic fog briefly spread across the European Union summit on Friday.

One word sent sparks flying between two of the biggest protagonists, British Prime Minister Theresa May and EU Commission chief Jean-Claude Juncker.

EU leaders have rebuffed May's request to sweeten the divorce agreement and help her win over a hostile U.K. Parliament, and Juncker complained to reporters Thursday about a political climate which was sometimes "nebulous, imprecise."

Juncker thought little more of it — until a clearly angry May confronted him at the summit table Friday.

The heated exchange was captured on video with no sound, but lip-readers reported that May said: "What did you call me? You called me nebulous." Juncker was seen shaking his head, apparently replying: "No I didn't."

Talks have been on a knife's edge for months for a divorce which both sides see as a defining moment in their history, with possibly hundreds of billions at stake depending on the outcome. So every word counts, however nebulous.

Juncker later explained that he was talking about the overall debate in Britain, where it is often hard to tell who is on which side, not referring to May personally.

May acknowledged Friday that she had a "robust" exchange with Juncker, but added: "That is the sort of discussion you are able to have when you've developed a working relationship and you work well together."

"What came out of that was his clarity that actually ... he had been talking about a general level of debate," she said.

Juncker was relieved. "I did not refer to her," he said. "I didn't, by the way, know that this word does exist in English."

It was time to kiss and make up. "In the course of the morning, after having checked what I said yesterday night, she was kissing me," Juncker said.