What is it called when the tense switches in the middle of a clause?
“But, sir,” said Harry, making valiant efforts not to sound argumentative, “it all comes to the same thing, doesn't it? I've got to try and kill him.”
‘Oh,’ said Slughorn, repressing a large belch. ‘Oh, dear. Yes, that was – was terrible indeed. Terrible ... terrible ...’
I'd like to learn more about the grammatical rules behind it, but I'm having a lot of trouble figuring out what it's called.