She slowed down, but not enough; and Keltham on Round One wasn't trying to hide any microsigns, but he also wasn't deliberately giving her any additional cues of how he was doing, like altering his own breathing or letting himself tense up. He was curious as to whether Carissa could read arousal microsigns herself.
The answer, as he predicted in advance, is no.
Keltham comes into her mouth the smallest amount he can, and when he's done doing that, grabs both her earlobes with his hands, bites with his fingernails, and twists.
He likes this part, Keltham thinks.