Keltham isn't trying to read her in very much detail - it's not like he even knows how to read 'level of pain', either 0 or a very very tiny number of people in Civilization would ever get any training on that - actually it's almost certainly 0 because never mind who needs to know, who would do the experiments to figure that out - anyways Keltham isn't trying to read her in very much detail, just enjoying himself.
He makes no effort to hold back his own rising pleasure, and he certainly isn't going to conceal his tells; he's curious about whether Carissa can read him, and what she does about that if he can. It would be a pity to tell her what to do, or even hint to her about what to do, before he's had any chance to observe what she does on her own.