Who Put That Backwash In My Cup?

650pm, kid's table, our house:

Emmy opens Chick Fil A cup full of lemonade.

Emmy: There are french fries in my lemon-lade
Me: Let me see.  (peeks inside not knowing what may be hiding in there).  Oh, that is backwash.
Emmy: Who put that backwash in my cup?
Me: Well honey, backwash happens when you take a drink but you aren't finished chewing your food.  So I guess it was you that put that backwash in your cup.
Emmy: Oh