Why does ζώου (animal) now have a 'υ' at the end? I thought it was just spelt as 'ζώο'?
Ζώο is the nominative case and ζώου is the genitive case (used like the 's for the possessive in English). For declensions see here.
Can someone in the know expand on the pronunciation difference between ζώο and ζώου?