The Master really hadn't believed he'd get punched in the face. He was helplessly tied to a post, it was the Doctor's job to defend him and he'd never let Jack hit him.

Except he did. And it really hurt. And it was harder than it looked to dodge it because he couldn't just move his head out of the way as he'd thought, by the time he tried that, Jack's fist was hitting his jaw, slamming his head back into the post by accident. The pain was exceptionally, as was the fact that in the process, he'd accidentally bitten his tongue. He barely had time to react afterwards but he fought against the handkerchief was vainly as he couldn't, trying to clench his exceptionally painful jaw... and failing.

Oh yeah, take away the one he had left? Nice. He was going to destroy that freak. He couldn't silence him for long, he was already working the bloody thing out of his mouth.