Why?

Eloise said, "Why?" for the first time this past week. 

A banana slug was in the cat food dish.  She has seen them before and still remembers the first time she ever saw one.  BUT this time she took a step back and looked at me, "hab it?" she asked.  "No," I said, "but you can touch it.  It's sticky." And then the why!  It surprised me. Did she really want to know why the slug was sticky?  So I asked her if that's what she meant.  "Yes." she said.  Ok.  I stammered around and said something about how the sticky stuff protects it.  I don't even know if that's true.  I've got to be more prepared next time.  I don't mind saying, " I don't know." but in my head while I was trying to answer Eloise's first Why, I was already grieving the passing of this first milestone.  I certainly didn't want her first ever Why to to be given an I don't know.