"A dog is der Hund the dog; a woman is die Frau the wom[an]; a horse
is das Pferd, the horse; now you put that dog in the Genitive case, &
is he the same dog he was before? No sir; he is des Hundes; put him in
the Dative case & what is he? Why, he is dem Hund. Now you snatch him
into the Accusative case & how is it with him? Why he is den Hunden?
But suppose he happens to be twins & you have to pluralize him – what
then? Why sir they'll swap that twin dog around thro' the four cases
till he'll think he's an entire International Dog Show all in his own
person. I don't like dogs, but I wouldn't treat a dog like that. I
wouldn't even treat a borrowed dog that way."
This is quoted in a biography of Mark Twain I'm reading.