A man went with his wife to a piano concert. They were seated together in the front row. After a while the man noticed that his wife had her head turned away from the pianist. He nudged her and asked her why she was looking away. She whispered that the pianist's fly was undone and his balls were showing, and she was too embaressed to look that way.

At the interval the husband got up and went over to the pianist and told him, "Do you know your balls are showing"?

The pianist replied, "No, but if you will hum it, I can probably play it".