Where Do They Learn These Words

This morning I took Ava to the potty and as I was getting her all cleaned up and off, this is the conversation that ensued:

Ava: “Do you have a gun in your hair?”

(I had my hair in my morning top knot. You know the one, a sort of pony tail but more of a really messy bun. The one you have before you take a shower and really “do” you hair. So I know my hair doesn’t look its best, but come on, people.)

Me: “What?! No!”

Ava, smiling: “What’s a gun?”

Well, thank goodness she had no idea what she was really talking about, but where in the world did that word come from and what prompted her to try it out at that moment?