Riddle:
Every day, a woman was seen crossing the border carrying bags of sand on a bicycle. After some time, the border police become suspicious and stop her, but found she only had sand on her, so they let her go.
Years later, they get a mysterious invitation for a party at a large villa. The owner comes out to greet them, it is the woman that has been crossing for years!
How did this happen?
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Hint:
The better question is: What was the woman really smuggling?