Daughter Andie used to do this long series of elephant that rounded back on the first joke she started with. It was just adorable. Wish i could find it or remember it.

knock knock
who's there
Amos
Amos who
Amosquito just bit me

knock knock
who's there
Andy
andy who
Andy bit me again

knock knock
who's there
oliver
oliver who
oliver sudden I'm being attacked

knock knock
who's there
sara
sara who
sara doctor around to give me something for the itching