Tony comes up to the Mexican border on his bicycle. He's got two large bags over his shoulders. Joe, the border guard, stops him and says, "What's in the bags?"
"Sand," answers Tony.
Joe says, "We'll just see about that. Get off the bike." Joe takes the bags and rips them apart; he empties them out and finds nothing in them but sand. He detains Tony overnight and has the sand analyzed, only to discover that there is nothing but pure sand in the bags.
Joe releases Tony, puts the sand into new bags, hefts them onto the man's shoulders, and lets him cross the border.
The next day, the same thing happens. Joe asks, "What have you got?" “Sand," says Tony.
Joe does his thorough examination and discovers that the bags contain nothing but sand. He gives the sand back to Tony, and Tony crosses the border on his bicycle.
This sequence of events is repeated every day for three years. Then Joe runs across Tony one day in a cantina in Mexico.
"Hey, buddy," says Joe, "I retired. I know you are 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?"
Tony sips his beer and says, "bicycles.”
