Teasing Store Clerk

A young boy went into a grocery store and asked the clerk for a can of cat food. The clerk, wanting to have some fun with the boy, told him that he could not sell him cat food unless he proved that he had a cat. The boy then left empty handed.
A few days later the same boy asked the same clerk for a can of dog food. Again the clerk replied that unless he could prove that he had a dog that he could not sell him the dog food.
A few days later the boy came in again and handed a paper bag to the clerk. The clerk put his hand in the bag and found that the bag was full of poop. The boy then said, “Can you sell me some toilet paper!”