Bahlool and a Slave

It is said that one of Haroun Rashid's slaves ate cheese, and a little cheese was stuck to his beard. Bahlool asked him, “What did you eat?”

The slave jokingly said, “I ate a pigeon.”

“I knew before you said so.”

“How did you know?”

Bahlool said, “I can see bird droppings on your beard.”