Twice a week a fraulein riding a bicycle crossed the German border carrying boxes filled with sand.
Each time the customs officials searched the boxes looking for contraband, but always in vain.
Sometimes they even emptied all the sand out, expecting to find some illegal item.
They racked their brains but never found anything untoward.
It was many years later, long after the fraulein had vanished from the scene, that they learned the truth.
She had been smuggling bicycles!