First was the repeating of the famous Carnegie Hall joke that rambunctious heard on a Sesame Street video "Howda get Carny Hall prakissprakissprakiss!" which he didn't "get" but understood was funny because it was treated as funny (a burgeoning class clown this one).
But now, the twins are beginning to master the rhythms of the knock-knock joke.
Just not the actual humor part:
Imperia: Knock Knock
Willow: Who's there?
I: Boo Who.
(long pause, a mixture of confusion and forgetting)
I: Don't cry!
I: Knock knock
W: Who's there?
W: (Knowing that a few steps have been skipped here) Orange who
I: Are you glad I didn't say lemon? (uproarious laughter)