[ Len doesn't know (or suspect) the half of it - but Arcade doesn't want to heap any more on him than he absolutely has to, right now. (There'll be too much of that, later, anyway.)

So he sticks to the actual parameters of that question, his interest obvious in spite of his best efforts to act as if he really doesn't have a clear fascination to exploit. ]

Flowers, with an unusual crystalline appearance. Just breathing in their scent creates a fairly powerful sedative effect.