who's there?

For a long time the children's favorite joke has the been the following:

Knock knock!
Who's there?
Banana! Knock knock!
Who's there?
Banana! Knock knock!
Who's there?
Orange!
Orange who?
Orange you glad I didn't say banana?

Recently they learned this new one:

Knock knock!
Who's there?
Interrupting cow.
Interrupting cow wh . . .
MOOOOOOOO!!!!!

As I was at the computer today, doing book inventory work, the two littlest ones sat behind me at the dining room table eating yogurt and telling each other these same old jokes. Apparently, my two-year-old was getting bored of the repetition. "Knock knock!" he exclaimed at his brother. "Who's there?" my five-year-old indulged. "Uh . . . interrupting orange!" At this I turned around just in time to see the punchline hit. "Interrupting orange . . ." his brother waited to let him interrupt but the look on two-year-old Storyteller's face was one of sudden panic " . . . who?"

"Um," Story started, uncertain, then decided that was perfect orange noise: "umumumumum!"

He repeated it a second time with a banana interrupting instead, but this time I guess he thought it through first because he was all prepared at the end and had the banana interrupt with opera music. It sang, "A lalalalalalala!"