Who You Gonna Call? ASSbusters!

My almost five-year-old granddaughter and I were watching "Ghostbusters" tonight. At one point during the movie she muttered, "Wow, that ghost is gonna kick their ass".

 I looked at that sweet little girl-child cuddled next to me who had just uttered the word, "ass" and I chastised, "Miley, that's a bad word".

She said, "I don't what to talk about it".

"Well, you are going to talk about it. Don't say 'ass' anymore. It's not nice. Say 'butt, okay?", I commanded in my sternest Gigi voice.

She looked at me questioningly. "Butt?" she asked, then she giggled. "You said

'butt'!", then she giggled some more.

I don't get it.  Maybe I'm just getting old. 

Or dumb. 

Or both.