This is too funny. Yday DS7 told this one and DD3 just rolled laughing the whole way home repeating it over and over...

Knock knock
Who's there
Cow
Cow who?
No Owls who Cows moo.

And...
Why do the birds fly south for the winter?


Because it is too far to walk.

And...
Why did the chicken cross the playground?


To get to the other slide.