Sitting back as Severus elaborates, it's clear that for a little while during this explanation, Lucius really has no idea what he's talking about, pallid eyes clear of much except scrutiny and puzzlement. But when one starts on about magical narcotics, it's a little difficult to miss the point no matter who is saying it.

His eyebrows go up, and he hesitates, before commenting;

"How very enterprising of you."

Which is code for that's awful and hilarious, but mostly due to knowing the Snape he knows, making this thing both different and yet strangely credible in a very off-beat, morbid way that would otherwise never happen. The injoke is clear in the comma of expression next to his mouth, the beginnings of smirk, but that's where it remains. "You sold to Muggles?"