Can't wait for homophones and palindromes

It always amazes me when my two children at 4ish and 2ish can have a coherent conversation with each other.

A few months ago, D was saying Who beeped the horn?, a favorite question of hers when she is riding in the car and hears someone honk the horn.
Meanwhile, S quickly said, Mooooom, D said Poopy the horn. I don't know if this is what she actually heard and she's trying to get clarification or she's engaging in a favorite activity of hers, getting her sister into trouble. Judging by her tone, it's more the latter.
Of course D is now bigger and smarter, very capable of defending herself (much more capable and mature than the days when S would ride a tricycle and D would crawl after her and sometimes D would get her fingers run on, poor thing). D retorted, No I didn't say POOPY the horn, I said WHO BEEPED the horn.
It always amuses me to hear them bickering comprehensibly considering how much nonsense they used to say.