What was he going on about? Severus hardly knew the other man, so he wasn't aware of any quirks or oddities that he might have. At that moment, he mildly regretted not getting to know the others in the Death Eater ranks. That was something that would need to be remedied in time, if only to gain more knowledge and to better anticipate his colleagues' reactions.
As it was, Severus didn't know if he should go along with this situation or just leave the potions with the other man and insist upon payment. Something in his voice, in the way that he was behaving, intrigued him enough to try and pry more information. If he let himself think about it, he might start tasting, perhaps even smelling, what Simon was. That wouldn't do. Brows lowered before he responded.
"Quite sure. Is this something that you sense often? The presence of cyanide is hardly something you would want to ignore."