Juan comes up to the Mexican border on his bicycle. Hes got two large bags over his shoulders.

The guard stops him and says, "Whats in the bags?""Sand," answered Juan.The guard says, "Well just 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 Juan overnight and has the sand analyzed, only to discover that there is nothing but pure sand in the bags.The guard releases Juan, puts the sand into new bags, hefts them onto the mans shoulders, and lets him cross the border.A week later, the same thing happens. The guard asks, "What have you got?""Sand," says Juan.The guard does his thorough examination and discovers that the bags contain nothing but sand.He gives the sand back to Juan, and Juan crosses the border on his bicycle.This sequence of events if repeated every day for three years. Finally, Juan doesnt show up one day and the guard meets him in a Cantina in Mexico."Hey, Buddy," says the guard, "I know you are smuggling something. Its driving me crazy. Its all I think about….. I cant sleep. Just between you and me, what are you smuggling?" Juan sips his beer and says, "Bicycles."