Findout my another Guest?

Birbal had been invited to lunch by a rich man.

Birbal went to the man's house and found him in a hall full of people. 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, "They are all employees except one man" and 

he is the only other guest here beside you, said the rich man.

Then a crafty look came on the man's face.

"Can you tell me which of them is the guest?" he asked.

"Maybe I could", said Birbal. "Talk to them as I observe them. Tell them a joke or something."

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

When he finished everyone laughed uproariously.

"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.

"Employees tend to laugh at any joke told by their employers," explained Birbal. "When I saw that this man was the only one not laughing at your joke, and in fact, looked positively bored, I at once knew he was your other guest."