Two Bags

Humphrey comes up to the Mexican border on his bicycle. He's got two large
bags over his shoulders. The guard stops him and says, "What's in the bags?"
"Sand," answered Humphrey. The guard says, "Well, we'll see about that. Get off
the bike." The guard takes the bags and rips them apart; he empties them out and
finds nothing in them but sand. He detains Humphrey overnight and has the sand
analyzed, only to discover that there is nothing but pure sand in the bags. The
guard releases Humphrey, puts the sand into new bags, hefts them onto the man's
shoulders, and lets him cross the border. A week later, the same thing happens.
The guard asks, "What have you got?" "Sand," says Humphrey. The guard does his
thorough examination and discovers that the bags contain nothing but sand. He
gives the sand backs to Humphrey, and watches him cross the border on his
bicycle. This sequence of events repeated everyday for three years. Finally,
Humphrey doesn't show up one day and the guard meets him in a Cantina in Mexico.
"Hey, Buddy," says the guard, "I know you're smuggling something. It's driving
me crazy. It's all I think about... I can't sleep. Just between you and me, what
are you smuggling?" Humphrey sips his beer and says, "bicycles."