Wet ones, Ozzy; if they've travelled any distance in an unheated baggage hold at high altitudes, I'd surely not like being hit by one at the end of the flight! Actually, not during flight, either; even if it's anti-freeze they're saturated with, they'd provide quite a smack. A frozen one, however -- ouch!
More relative to the original subject, slip the stuff into somones bag at an entry or transfer point and have someone pull it back out during another transfer; if the transfer extraction doesn't work and the stuff is discovered, some poor dupe gets shafted instead of them -- better luck next time. What do smugglers care about what harm they cause someone else anymore than most any other criminal? One of my closest (FORMALLY - haven't seen him for a long while while, quite fortunately) cousins nearly got me arrested (maybe more than once since he'd started some time before I found out about it). They only care about getting away with what they're doing and everything else is just consequential.