Why?

My two-year-old is a fountain of questions.

Today we were visiting with Grandma Gin and he wanted to know about a rock that was on her bookshelf. "What's that rock doin' Grandma?"

She explained that it was a rock that is called tuff.
"What tuff?"

She explained that tuff forms during volcanic eruptions.
"What that?"

She explained that volcanoes are openings in the earth that allow lava to escape, sometimes in a large explosion.
"Why?"

She explained that sometimes there aren't enough virgins to sacrifice.