Clare logged hours of tutoring today. She did her very best to teach her unwilling sister about knock knock jokes. Here's her favorite:

Knock knock.
Who's there?
Cow.
Cow who?
Interrupting cow. MOO!

She was relentless. Only Ella didn't relent. So it sounded like this:
"I'll say 'knock knock' and you say 'who's there?' Then I'll say 'cow' and you say...Ella! Are you listening?! Can you SAY interrupting cow?! Ella!"
And Ella had her fingers in her ears the ENTIRE TIME. Every now and then, she would grin and say "NO."
After thirty torturous minutes of this (during which time I had half crawled up ONTO the front dash in my efforts to escape them and listen to NPR), Ella finally gave in.
"Knock knock." says Clare
To which Ella replies "Moo who?"
"Ella! You say who's there!"
"Cow."
"No! You say who's there!"
"no. Gock gock."
"No! Ella! 'Who's there?'"
"Cow."
"ELLA! You don't say 'cow'!"
"Inneruckik cow."