A fellow tries to cross the Mexican border on a bicycle with two big bags
balanced on his shoulders.  The guard asks, "What's in the bags?"

The fellow says, "Sand!"

The guard wants to examine them.  The fellow gets off the bike, places the
bags on the ground, opens them up, and the guard inspects... only to find
sand.  The fellow packs the sand, places the bags on his shoulders, and
pedals the bike across the border.

Two weeks later, the same situation is repeated...

"What have you there?"

"Sand"

"We want to examine."

Same results... nothing but sand and the fellow is on his way again.

Every two weeks for six months the inspections continue.  Finally, one week
the fellow didn't show up.  However, the guard sees him downtown and says to
the fellow, "Buddy, you had us crazy.  We sort of knew you were smuggling
something.  I won't say anything what were you smuggling?"

The fellow says, "Bicycles."
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