Slippery Fish

Once there was a fish so slippery that nobody ever caught it. In fact, there was a whole school of this fish. And nobody except one man ever caught sight of them because they stayed at the bottom of their sea. The man who saw them tried to catch one but they slipped through his grasp. Others dove down there too but never saw them. So they thought the man who spoke of slippery fish made it all up. He dove back down there to prove it to them but he could never catch them. And when he brought others with him, the fish disappeared altogether and so he began to wonder if he had ever seen them at all.