Who was Nana? How did Toto tease Nana? 

Solution
Nana was the family donkey, well-behaved and docile in nature. Toto was kept in the stable with Nana, where they both used to fight since Toto was naughty and kept on teasing Nana. He used to bite onto her long ears with his sharp little teeth and Nana could bear him no longer.