"You want me to just think of one and you try and guess what I'm thinking?" I asked.
"Yeah," he said.
"Okay," I told him, "I will concentrate on one moon phase and you guess which one I'm thinking of."
I then focused on picturing one particular moon phase and repeated its name in my head. Guess what? He guessed each one correctly? Coincidence? Maybe. But it was cool at the time!
Just don't think too loud around him just in case.