At a party, the host was getting worried because there were too many people and not enough refreshments. She was sure that not all of them had been invited but didn’t know how to tell which ones were the crashers.
Then her husband got an idea. He turned to the crowd of the guests and said, “Will everyone from the bride’s side of the family stand up please?”
About 20 people stood.
Then he asked, “Will everyone from the groom’s side of the family stand up please?”
About 25 people stood up.
Then he smiled and said, “Will everyone who stood please leave. This is a ‘Birthday Party’!”