Here's a little background to the dialogue: Miller is 5 and is a friend's son. The unnamed girl is around 8 and is a neighbor of Miller's. She has a dog named Willie. Here's the conversation I overheard yesterday while the two of them were playing with the dog.
Miller: I have a cat named Buddy.
Miller: Not Willie. Buddy.
Miller: No. Buddy. Not Willie.
Miller: NO. His name isn't Willie. It's Buddy.
Miller: NO. IT'S NOT WILLIE. IT'S BUDDY!
I stepped in at that point and explained that she was saying 'really', not 'Willie'. I thought it was best before he beat up a girl.