He decided to enter the first door he found open: a carpenter's shop.
"Hello!" said the carpenter.
"Hello!" replied Nasruddin. "Did you see me just now walk into your shop?"
"Yes," replied the carpenter, not sure what Nasruddin was getting at.
"And have you ever seen me before?" asked Nasruddin.
"No, I've never seen you before," admitted the carpenter.
"Then how did you know it was me?"
Inspired by: Mulla's Donkey and Other Friends by Mehdi Nakosteen
Notes: This story is on p. 82 of the book.