Emperor Akbar once ruled over India. He was a wise and intelligent ruler, and he had in his court the Nine Gems, his nine advisors, who were each known for a particular skill. One of these Gems was Birbal, known for his wit and wisdom. The story below is one of the examples of his wit. Do you have it in you to find out the answer?

Birbal had been invited to lunch by a rich man. Birbal went to the man's house and found that the lunch was in fact a big party and there were many people around.

His host greeted him warmly.

"I did not know there would be so many guests," said Birbal, who hated large gatherings.

"They are not guests," said the man, "They are my employees, all except one man. He is the only other guest here beside you."

Then the host saw the perfect opportunity to test Birbal's wit and wisdom. "Can you tell me which of them is the guest?" he asked.

"Maybe I could. I will definitely give it a try," said Birbal. "Talk to them as I observe them. And tell them a joke."

The man told a joke that Birbal thought was perhaps the worst he had heard in a long time.

By the time the host finished telling the joke, Birbal knew who the guest was.

"Well," said the rich man. "I've told my joke. Now tell me who my other guest is."

Birbal pointed out the man to him.

"How did you know?" asked his host, amazed.

What was Birbal's reply?