An old woman goes into a supermarket to buy cat food. Knowing that times are hard, the cashier is sure that the old woman is buying the cat food to eat it herself.
"Before I can let you buy that, I need you to prove to me that you own a cat."
The old woman is upset, and tries to argue, but the cashier doesn't let up. Later that day, the old woman returns with her cat in a carrier, and is allowed to buy cat food.
The next day, the old woman goes to the same supermarket to buy dog food. The cashier can't believe that she has both a cat and a dog and again tells the old woman that she needs to prove that she owns a dog. The old woman leaves and comes back with a tiny dog, and is allowed to buy dog food.
A few days pass, and the old woman returns to the supermarket, but instead of going to the aisles, goes straight to the cashier and hands the cashier a paper bag. The old woman motions for the cashier to open it and look inside. The cashier does this, and while doing so, catches a whiff of its contents.
Recoiling, he exclaims, "Eww, this smells like crap!"
The old woman says, "It is. Now, let me buy this toilet paper!”