Inside joke

As I got Nikko ready for school, he made a funny face where he gritted his teeth, jutting out his jaw, and shook his head quickly back and forth as if he were vibrating. I copied him except I opened my eyes wider to exaggerate the expression. He looked at my face and totally cracked up. Then he copied ME. Then I copied HIM. And we had this nice little exchanged that made us laugh together before school. We did it a few times later in the day and it was almost like an inside joke for us to share. That was a nice part to my day.