Grandma by Any Other Name

Toots, our granddaughter, is experimenting with our grandparent names. For example, she has always called me Mimi and hubby Papa. But now she says Grandmother, Grandma, Granny, Nana for me and Poppy for Grandpa. I told her that is fine, but that I don't prefer Granny. So guess what she lets slip out? She smiles and quickly says, "I mean Nana." I suppose she hears all those choices from her pre-school and daycare friends. I have been playing along with her and decided to start calling her by her middle name, shortened middle name, etc. She just grinned and commented that I was doing what she was doing with names. How did she get so smart at 5?