There was a man who lived near the border of two countries in Europe. Every day, for work (or so he claimed), he crossed the border with a wheelbarrow full of straw.
And every day, the customs officer at the border searched through the straw, convinced this man was smuggling something. But every day, there was nothing in the wheelbarrow except for straw.
This went on for years and years, with the customs officer never finding anything.
Some time later, both men had retired. But they happened to meet up at a social. The customs officer turned to the man and said "Look, I know you were smuggling something. But I have to admit, I've no idea what! I don't work for customs any more, so can you PLEASE tell me what it was!!"
The man replied "Wheelbarrows".