He swallows when she stops, realizing he was genuinely scared for a moment there. How does he even explain this to a psycho like her? In some ways, it's easier because she doesn't care about him, not the way other people do. But in others it's harder, like she's untouchable. Like being weak in front of Elektra is the last thing he would ever want to do, even if it's more for self-preservation than to save his own feelings. Would you bare your throat to a wild tigress?

"I can't feel anything. I won't know how hard I'm hitting you." Or how hard she's hitting him. He'll be even harder to stop than usual, but he knows she's into that sort of thing.