Abbie is notorious for, "Knock, Knock" and getting no answer...
But she is gradually putting a second line in. "Who is there?" Abbie: "Uh, (looking around the room) Shoe!" (Mama smiles politely)
Abbie: Knock, Knock.
Mama: Who's there?
Abbie: (Looking around the room) Owl!
Mama: Owl who?
Abbie: No, Owls say who!
Mama and Maggie laughed and told her what a good joke!!!