While crossing the US-Mexican border on his bicycle, the man was stopped by a guard who pointed to two sacks he had on his shoulders. "What's in the bags?" "Sand," said the cyclist. "If you don't mind sir, we'll just take a look at those." The cyclist did as he was told. The guards searched the bags but could find nothing but sand. He continued across the border. Next week the same thing happened. Again the guards demanded to see the two bags, which contained nothing but sand. This went on every week for six months until it stopped suddenly. Some time later one of the guards happened to meet the cyclist on the street. "Say, you sure drove us crazy. We knew you were smuggling something across the border. I promise I won't rat--I just gotta know: what were you smuggling?" "Bicycles."