understanding the concept of "boo"

Peek-a-boo is one of Ronin's favorite things, but now it has transformed into a game that is more like hide-and-seek. He likes to hide behind the chair, sneak around the corner, then pop his little head out and say, "Boo!" He likes to do this in the morning when he wakes up too: I will peek my head around the door and when he sees me, he says, "Boo!"

This morning, I was sitting in the chair that Ronin likes to hide behind, so he must have been a little frustrated that he wasn't finding me when he peeked around the corner. From the chair I hear him yell, "Mommy! Mommy!" Once I looked down, he smiled, extremely pleased I had found him and then said, "Boo!" Not quite how it works, but he's getting there.