Crossing the border

While crossing the US-Mexican border on his bicycle, the man was stopped by a guard who pointed to two sacks the man had on his shoulders. "What's in the bags?", asked the guard.
"Sand," said the cyclist.
"Get them off - we'll take a look," said the guard.
The Cyclist did as he was told, emptied the bags, and proving they contained nothing but sand, reloaded the bags, put them on his shoulders and continued across the border.
Two weeks later, the same thing happened. Again the guard demanded to see the two bags, which again contained nothing but sand. This went on every week for six months, until one day the cyclist with the sand bags failed to appear.
A few days later, the guard happened to meet the cyclist downtown. "Say friend, you sure had us crazy", said the guard. "We knew you were smuggling something across the border. I won't say a word - but what is it you were smuggling?" "Bicycles!"