Haha. Because people think that the people at custom's just aren't as smart as smugglers.
It's like people who take their wallets to the beach. When they go into the water, they put their money in the toe part of their shoe. "Geez, nobody will think to look there for it." LoL
Best advice is to just not do it. And if you're going to do it - never talk about, cuz it never happened.
But on a serious note. The best way to get drugs across the border is to shove it up your dogs ass. That way, if they have drug sniffing dogs, you can just say your sexy dog is in heat. <grin>