Why you not know any more whys?

Daniel started asking "Why????" several weeks ago. At first he would accept the first thing we said and go on to the next subject. As time goes on, he just continually asks why after each explanation. Finally, I just had to say, "That's all. I don't have any more explanations about that." That seemed to stop him for a few days. Then, he came up with a new comment- "Why you not know any more whys, Mama?"