Severus watched the girl carefully, as she pondered what he'd said for the longest time. Numerous different emotions seemed to cross her face in the interim, and if he'd known her better, he might have been able to identify them. As it was, since they'd only just met face-to-face, he simply watched with interest. Until, of course, she finally requested more information.
"In the simplest form, the discipline involves merely clearing one's mind of all emotion," he began, with a slight shrug. "As one becomes more practiced at manipulating the emotions, however, one can suppress selected thoughts and feelings." In his case, he normally chose thoughts or feelings that would contradict the lies he had been telling the Dark Lord at any particular time, since his mind's being entirely blank would have been suspicious. "For you, I think suppressing any memories or thoughts that cause you particular agitation would be beneficial."