how NOT to teach a 4 year old a "knock knock" joke.

mommy - "knock, knock" (on the wall)
elijah - "knock, knock" (on the wall)
mommy - "no, you say who's there"
elijah - "who's there"
mommy - "banana"
elijah - "banana"
mommy - "no, you say banana who"
elijah - "banana who"

- repeat from beginning-

mommy - "no, you say banana who"
elijah - "that's not a door that's a wall!"