Isn't It Obvious?

The other night at dinner, Big Sister announced that she was spitting her water in her cup. The following conversation ensued.

Me: "Why are you spitting your water in your cup?"

Big Sister: (Looking at me as though I had four heads) "Because I wouldn't want to spit it on the table."

Me: "Oh, okay."

It was hard to argue with that logic. I'll probably have to stop that little trick at some point, but she was the only one left at the table. I have a hard time stopping entertainment that keeps her occupied and doesn't make a mess. What's a little spittle in a cup when we're used to bodily fluids on the floor?