Why?

Joanna is inquisitive, and has well and truly discovered the "why" question. What surprises me at the moment isn't so much the "why" questions, but the "why" question. She'll ask the same question repeatedly, with a short gap between questions. Currently it is "Why was the lady sad?", to which the stock answer is "because the bear grew up and had to go away" (The film Open season). She got more and more persistent yesterday with the "whys", and it appeared our answers were lacking, as she ended up shouting in frustration "but just WHY?".