In most cases drugs are detected by dogs, which is why smugglers do stuff like seal it in coffee bags, liquids, etc. Surprisingly, it rarely masks the smell enough to fool a dog.
Anyway, hopefully customs folks won't start ripping appart any sword they find, looking for drugs. IMO it would be pretty dumb to do that, as they'd go crazy doing it while shipments of painted plaster yams sneak through.
