Boo!

A recent conversation

Aaron (looking at a scab on Mike's thumb): What is that?
Daddy: An ouchie. Can you say ouchie?
Aaron: What is that?
Daddy: Ouchie.
Aaron: What is that?
Mama: Let's try something different... it's a boo-boo. Can you say boo-boo?
Aaron (covers his eyes with his hands, then quickly pulls them away): Boo!