How can you prove that you are a fox?

Once upon a time there was a fox who met a young rabbit in the woods. The rabbit said: "What are you?" The fox said: "I am a fox, and I could eat you up if I wanted to."

'How can you prove that you are a fox?" asked the rabbit. The fox didn't know what to say, because in the past rabbits had always run from him without such enquiries.

Then the rabbit said: "If you can show me written proof that you are fox, I'll believe you."

So the fox trotted off to the lion, who gave him a certificate that he was a fox.

When he got back to where the rabbit was waiting, the fox started to read out the document. It is also pleased him that he dwelt over the paragraph with lingering delight. Meanwhile, getting the gist of the message from the first few lines, the rabbit ran down a burrow and was never seen again.

The fox went back to the lion's den, where he saw a deer talking to the lion. The deer was saying:

"I want to see written proof that you are lion..."

The lion said: "When I am not hungry, I don't need to bother. When I am hungry, you don't need anything in writing."

The fox said to the lion: "Why didn't you tell me to do that, when I asked for the certificate for the rabbit?"
"My dear friend," said the lion, "you should have said that it was requested by a rabbit. I thought it must be for a stupid human beings, from whom some of these idiotic animals have learned this pastime."