Translate this joke.

One day, an old woman went to a grocery store to buy cat food, so she took three bags to the cashier. But the cashier said, I'm sorry, I can't sell you cat food because you have no proof that you have a cat. Nowadays, many old people always buy cat food for themselves instead of cats, so the government requires you to have proof that you own a cat before selling it to you.

The old woman came home, picked up the cat and went to the store, and really sold her cat food.

The next day, she wanted to buy some dog food, and the cashier told her that I can't sell it to you unless you have a dog certificate, because many old people often buy dog food for themselves and don't give it to dogs.

So she brought the dog again and sold her dog food.

Another day, the woman brought a box with a hole and asked the cashier to put her hand into the hole. The lady refused, saying, "No, there may be a snake in it." But that woman promised that there was nothing in it and it wouldn't hurt you. So the young lady put her finger in, and then stretched it out and said, "Why does it smell like shit!" " "Then the old woman said proudly," Can I buy three rolls of toilet paper now? "