...on hand? Something about that statement strikes Foster as incongruous, but he doesn't concretely know 'why.' He has to think about it for a few.

"...."

Why would Ginko need it on hand--more specifically, why Ginko specifically? After a second or two, he turns it on its head, and reaches his conclusion:

"... do you attract them or something?" Wait-- "If that's how it works, is it necessary to smoke it at all, then?"

With other repellents, burning the leaves releases either a chemical or magical energy.